You only earn points for eliminating foes when you destroy your opponent's warriors. You have only one opponent in the Clans Battle — you can view them in the Info tab of the Competition window.

If you have an ally, you can help them by sending reinforcements or troops on an Onslaught. Your ally's opponent isn't your opponent, however, so you won't earn points for killing your ally's opponent's warriors.

However, you will earn points if you eliminate troops led by jötunns in your ally's Stronghold.

If you attack your opponent's Stronghold, but only their ally's troops are there, you won't earn points for killing these warriors.

You can read other rules regarding scoring points in the "Why didn't I receive any points in the Competition?" section.