To revive your pet once it has been killed, you have a few options;
1. Target your pet and double click on a Resurrection Scroll
No lost experience will be recovered
2. Have a cleric join your group and they can use Resurrection skill
Some lost experience will be recovered
3. Target your pet and double click on a Creature Resurrection Scroll or Spellbook (there's no difference except weight & name)
All experience lost when your pet died will be recovered.
If your pet's corpse has faded away, re-Summon it just as you would to begin with, then follow one of the steps above.