In NFHS a pass is intercepted in the endzone. What is the call. Touchback or no touchback?

not enough information here - what happened after he intercepted - was he tackled? did he kneel down? did he run out of bounds? did he run into the field of play?

If he intercepted the ball in the endzone - and was down, then yes you have a touchback.

Rule 8-5-3...It is a touchback when:

D. a forward pass is intercepted in B's end zone and becomes DEAD there in B's possession.

although B has the right to run the ball out or knee the ball down, so take a chance of making 20 or knee it for a free 20.

THe ball does not become dead, he can run it or take a knee.

Canadian Ruling
 

You didn't say which EZ the pass was intercepted in.

If the pass was intercepted in A's EZ, score a TD. This is the ultimate, I think.

If the pass was intercepted in B's EZ, and he goes dead in the EZ, B 1D/10 @ B-20. If the player gets out of the EZ, B 1D/10 @ PBD.