Well you'd have to look for rejected blocks in your bitcoin debug.log
Give it a while
Also the network hash rate will probably drop a bit - but that won't be obvious for a while either.
The pools list at btc.com may or may not show the split correctly ... who knows how they come up with the numbers there
I sent them the details for KanoPool a while ago and they've still done nothing to fix that ...

Edit: blockchair.com was supposed to have a browser at fork time ... but that clearly didn't happen