Your questions are off-topic of this blog, but I will answer it here. I wish you would have asked the question on a recent blog that is more related to the subject, such as McAfee’s Dick Math: illuminating Bitcoin’s ACCELERATING price or Bitcoin’s Whiplash Bear Trap. I read your other comment on my older blog, but it was not as detailed as this comment of yours so I decided to reply to this one.
Thanks for often recommending that 
Or does one have to check that the btc one has were only on legacy (1...) addresses?
How can one do that on CEX, without DEX? (cuz there aint real yet..)
I guess one basically has to trade one's segwit btc to the exchange, trade them, withdraw and look into the coins history if they were on segwit addresses anytime? If yes, repeat until one has only coins which only were on legacy addresses..?
You likely can’t utilize a wallet on a centralized exchange and expect to come out of this without losing everything.
Generate legacy addresses (those that begin with 1) on a wallet you control on your own computer or device. All Trezors have an option for legacy wallets. Send the BTC from the centralized exchange wallet to the legacy address for the wallet you control on your own computer or device.
To later transfer the Bitcoin from your wallet to someone else, then sign a transaction with your wallet and use some way to send it to the Bitcoin network. For example, Trezor includes a wallet service does this for you.
Bear in mind though that later during the posited chaos coming, if the miners’ mempool is congested, then your transaction may be delayed or never put in a block. So make sure your addresses hold significant Bitcoin (e.g. 1+ BTC) each so that when you transfer, then you can afford to include a high enough transaction fee. Bear in mind though that while the posited SegWit donations are filling up all the blocks (for months or years?) then transaction fees may be skyhigh. I have not tried to compute how high, but given the largest UTXO accounts will be taken first, initially transaction fees could perhaps be even in excess of 1 or 10 Bitcoins! We’ll see...
Is it already safe to just hodl one's btc on legacy (1....) addresses?
Due to recent epiphanies about involuntary income taxes on coming airdropped Core Bitcoin tokens and SegWit lineage tokens eventually frozen by miners, that’s no longer sufficient (archived).
As the above linked post explains, you now have to be concerned with involuntary income taxation due to the airdropped Core tokens at their pre-crash value and also inability to get any transaction accepted on the legacy Bitcoin chain after the fork-off, because of congestion due to the taking of the 7+ million SegWit UTXO which may go on for some considerable time (for months or years?). And by the time you get your legacy Bitcoin transaction onto to the blockchain, the price may have cratered into a cryptowinter again and/or the regulations and capital controls on converting to fiat may be impossible for us to navigate.
The newest revelation about SegWit lineage tokens being eventually frozen comes from a recent post by the user who had created the Long-term advance notice thread:
[…] at last any coin ever moved through a sw address is frozen […]
Remember Craig Wright recently warned that global coordination such as via the intergovernmental global agency Financial Action Task Force (FATF) will force the miners to freeze Bitcoins which were involved in crime.
They will destroy us both with income taxes for the involuntary airdrop, the inability to spend after the attack because blocks will be full of donated SegWit tokens, and then later the FATF will declare that all SegWit lineage coins must be frozen because they possibly were involved in off-chain Lightning Networks (LN) crap which is not fully traceable! Ah fuck! Why did I not think of that. Now I totally understand what Craig has been warning[foaming at the mouth] about.
We are fucked. Only virgin mined BTC that had no SegWit lineage will remain fungible.
The powers-that-be are genuinely going to take back control over the entire money supply. And the money supply will be drastically shrunk to perhaps less than 5 million BTC. This will increase scarcity and cause the price to skyrocket.
So the miners who take the SegWit donations will then spend them and everyone will assume those tokens will have value because they are of course forced to be transferred legacy addresses. But later those will be frozen due to their SegWit lineage, after the miners have long since sold them.
Imagine you will have this huge involuntary income tax bill and never ever be able to unfreeze your legacy BTC to raise revenue. The powers-that-be are going to burn the fingertips of the goldbugs and cryptobugs up to their armpits.
We would be much better off selling before the halving and buying mining equipment. But again I feel this entire Bitcoin thing is just too fucking dangerous to mess with after the halving even for small-scale mining.
Sell and go away just before the halving. Maybe thinking about mining or reinvesting in some anonymous altcoin with a clear future, if there is such a thing by then.
In short, we are being kicked off of Bitcoin and there is maybe nothing we can do to stop that. I posit that Bitcoin will be only for $multi-millionaires and $billionaires who are subservient to the powers-that-be. Something even 
My nemesis @nutildah wrote:
There is zero actual truth behind this. We're talking about a 51% attack, in which it would be retarded to think the price of BTC would come out of it unscathed. However, the chances of a 51% attack happening in BTC are next to nothing.
Even if it did happen, assuredly the bitcoin community would reorganize and go with the chain where the attack didn't happen. So "anyone can spend" would only be in effect for as long as people were willing to buy coins on the wrong chain. It would be chaotic for a few weeks, and yes, the price of BTC would plummet, along with all other coins. It could take years for confidence to rebuild afterward. However, I'm willing to bet anybody that this will NOT happen, EVER.
There will not be any 50+% attack because nothing in the legacy protocol will be violated by taking the SegWit as “anyone can spend” donations. No double-spends, no censorship and no theft from the perspective of the legacy protocol, although the FATF and the law may view the SegWit as tainted which is a separate matter. Satoshi’s immutable legacy protocol does not recognize Core addresses as being protected by any signature. Thus anyone can spend them (that is until perhaps some future FATF demand forces miners to freeze them in the future). So legacy miners will spend the donated SegWit “anyone can spend” UTXO to themselves.
The Core protocol as a soft-fork was the Trojan horse attack. The miners will be forced to mine the legacy protocol because the value of their minted block reward revenue will plummet (as @nutildah admits) due to the hard fork (and Craig selling ~1 million Core Bitcoins on exchanges to fulfill his intentionally self-imposed/feigned/fabricated court case judgement, c.f. also) and so the miners will have no choice but to mine on the chain where they can get extra revenue from SegWit “anyone can spend” donations to subsidize their mining profits. Actually someone should post this paragraph as an explanation to BCTalk, but do not attribute it to me because some gatekeepers at BCTalk hate for me to tell the truth there. Perhaps @OROBTC should finally be a team player and post a link to this instead of posting nonsense. But I really don’t care. Let them fool all the witless technologically illiterate fools (i.e. who lack the requisite technological knowledge) in the W.O. thread who disrespect me so much they do not even try to ask me for an explanation and instead rely on W.O. “members”. Ha! I will get the last laugh on this one.
Astute summary by @jbreher, although I doubt the technologically handicapped W.O. readers comprehend how to unpack the meaning.
Even the myopic, high pride, overconfident, precious metals bug
¹ I began the factual rebuke of his lies about Armstrong in my recent blog Trillionaire Fund Manager Martin Armstrong Was Framed By Our Corrupt Government. I am planning to write a follow-up blog to detail Armstrong’s models and trading record to further refute the lies about it.
RE: Trillionaire Fund Manager Martin Armstrong Was Framed By Our Corrupt Government