knight endgame checkmate

Can someone checkmate with the only pieces left two knights ?

In theory yes, in practice no

If the losing side has a pawn, in practice sometimes too, depending where the pawn is

Timing is everything

It's pretty complicated, I think, much arder than B+N.

In the Diagram, White wins in 41 moves, according to the tablebase.

With the pawn on c6, it's also a win. Nut with the pawn on c5 or c6,  it's a draw. It takes a better player than me to understand that.

with three knights mate can be forced in 31 moves (providing the lone king can't quickly win a knight)  

LongIslandMark: that's exactly right. For example, stronger King on g3, weaker King on g1, Knight on e2 checking, Knight on e3 covering the escape to f1, the weaker King has to go in the corner but then the e3 Knight takes two moves to mate the King now on h1 and after the first of those moves it's stalemate unless the weaker King also has a superfluous pawn to move.

edit: The advancing student can explain why this is a bad example. 

So it is pssible with a pawn for rival

Just to make a puzzle from LongIslandMark's diagram: