Two nails on one side and one on the other at both ends of the stud.
Doesn't matter which side has 2 and doesn't matter if they are the same or
opposite top to bottom.

Crusty old timers in our area do it that way. They also prefer the sequence
single nail center top and bottom, then opposite side two nails whichever is
handier. The two single nails allow easier fudging of the stud position before
the other nails really anchor it down.
If you dare ask them why they don't use 4 nails, be prepared for a long
harangue about the lousy lumber you're providing. HTH

Joe