For example, if I'm printing an interface by calling print(), and then, It will call printiface(), I'm wondering what does go actually between these two statements.
From what I could gather, print calls turn into printstring, printiface, etc. at compile time. If you want to look at how print code is generated, you could be interested in this code in src/cmd/gc/walk.c.
That method printiface() is mainly called by ifaceI2T(), ifaceI2I(), ifaceeq(), printinter().
So you can see more in runtime/iface.c