As far as I know, there isn't a way to very quickly check for hacked Pokemon, you'll most likely to have to go through all of them to tell if they are hacked. However, there are a few easy ways to check if Pokemon are hacked.
- Check it's moves, if the Pokemon has a move that it can't learn, it's hacked.
- Check it's ability, if the Pokemon has an ability that it cant have, it's hacked.
- If it's an event only Pokemon, check it's OT, if it has an OT that isn't possible, it's hacked (Note that some event exclusive Pokemon have had events in which the OT is the original owner's OT.)
- See if anything is suspicious, if you have a shiny 6 IV Pokemon with a beneficial nature, there is a high possibility that it's hacked, this doesn't necessarily mean that it is hacked, however.
Hope this helps!