attacking on the jump :

[666bender]

with spring attack or fly by - its easy.
without - not so....

lets take this scene:
a creature is 10 feet up.
i got +60 jump.

option 1:
1. move action = jump check
2. if i reach i can attack
3. i fall (getting damage)

option 2: (easy)
1. same as option 1 but need a trio feat for spring attack to do (move before and after)

option 3:
same as option 1 BUT:
1. we look at combat like a river, not a a round-per-round event.
2. move = jump check
3. i attack and round ends.
4. NEXT round i start by falling down

also, another matter: can one jump and grapple/grab ? how is that handled ?

[MendedWall12]

You might want to take a look at Rite Publishing's 101 New Skill Uses. It has a mechanic for just this kind of maneuver. Besides my Core Rulebook, this is the most used book at my table.