Some airlines publish this info on their sites. I know AC does for example. Also almost all alliance members in *A interline with/between each other and so do most of the other members in SkyTeam and OW.
One key point to remember is if your journey includes more than two airlines, all of them need to interline with each other! i.e. in itinerary with airlines A-B-C, it's not enough if B-C have interline, but also A-B and A-C should interline as well.