if you have u rcompanion out, and kill a mob, you will see on your log smth along the line of:

"You gained 200 conjurer experience points (+100%)
You gained 100 experience points"

...and this is not present when your companion is not out.

So i am inclined to to believe that the 100 experience points (in this case), which is the base of the xperience point you gained from killing, is what the companion got.