This steemit-post has the necessary information to know if you're on a fork or not:
https://steemit.com/gridcoin/@cautilus/psa-what-to-do-if-your-difficulty-0-1-and-or-net-weight-300-000-i-e-if-you-re-on-a-fork-windows

But here simple steps cause the wall of text in the linked post is not really readable:

1. Open the wallet-console (Wallet -> Help -> Debug Window -> Console-Tab in new window)
2. Enter "getblockhash 123" without the quotes and change the 123 to the latest block you see in your wallet (under total, above difficulty) and you'll get the hash for this block
3. Go to website gridcoin.network and search for this block number
4. Compare the returned hash with the one in your console
5. If both are the same, you're not on a fork (at least if gridcoin.network is not on a fork)
6. If they are not the same, repeat the steps with a lower block number till you find the last matching hash
7. Go again to your console and enter "reorganize A1B2C3" without quotes and replace A1B2C3 with the last matching hash (not the block number!)
8. Wait till the wallet is in sync
9. If you're then again on a fork (Difficulty=0.000), repeat this steps and find the next invalid hash

The only easy way (as far I know) to see the different chains is to use the gridcoinstats status-page (under About -> Gridcoinstats.eu).