Submarines in WWII could engage eachother while surfaced or at periscope depth, but not while deeply submerged.

A surfaced sub could engage another surfaced sub.
A submerged sub at periscope depth could engage another surfaced sub
A surfaced sub could fire at a submrged sub at periscope depth
A sub at periscope depth could engage another sub at periscope depth.

All these scenarios happened in WWII. The first two were common, the third rare, the last happened only once.

There was no case of a sub at deep submergence (below periscope depth) attacking another sub in WWI or WWII.

The sub could not accurately get targeting information from hydrophones, and the torpedoes had to be set to run at a certain constant depth - no more than 40 or 50 feet. There was no way to fire a torpedo at a deeply submerged sub.

Basically subs could engage other subs the same way as they engaged other, surface, vessels. No underwater sub vs sub battles.

At the very end the XXI U-boat hydrophones and some of the more advanced, acoustic homing torpedoes were making it possible to do so, but they did not reach action in the war.