If you're talking about actual xp that is seen in the xp bar, then you could do something such as:

Code (Text):

1. on death:
2.     victim is not player
3.     if victim is cow:
4.         add 1 to total experience of player
5.     else if victim is enderman:
6.         add 10 to total experience of player

Afaik, Skript doesn't have an actual player experience expression (correct me if I'm wrong!). This total experience expression is from the addon SkBee.

And for leveling up:

Code (Text):

1. on player level up:
2.     #do stuff