Building new block wall and need a couple of outlets in the wall. How is this done?

Is this going to be Poured with concrete?
If it going to be plastered, you don't have to be as accurate.
If Bare block is finished surface, then I would drill out the corners with a carbide bit, then a die grinder, I do it all the time, works well.

Is it going to be firred out?
Is the conduit coming up into one of the cells?

For 2 outlets, you could Lay 2 courses of block and notch the block from 1 receptacle to the other.