Can you disarm or trip on a cleave attack (either on the triggering attack or on the bonus attack)?
One of my players has a build which might rely on it.
I would say yes since the wording is an additional attack and from combat maneuver section:
When performing a combat maneuver, you must use an action appropriate to the maneuver you are attempting to perform. While many combat maneuvers can be performed as part of an attack action, full-attack action, or attack of opportunity (in place of a melee attack), others require a specific action.
Emphasis mine.
Depends on the action description in the CM. If it "replaces an attack", then yes, but if it requires an action of its own, no.
Bull Rush: No
Disarm: Yes
Grapple: No
Overrun: No
Sunder: No
Trip: Yes
I exclude Sunder from that list, because the attacks in Cleave are not the attack action, they are the Cleave action.