You can make oxygen with either eight hydrogens (annoying method) or with nitrogen plus hydrogen (easy method).
One waldo should make the oxygen and the other should make the triple bonded nitrogen molecule. The easiest way to make the triple nitrogen is to use a drive-thru bonder.
The first waldo should grab a nitrogen and get out of the way and take it up to the fuser which, naturally, is placed on the hydrogen input. It should call Sync to allow the other molecule to quickly pull out a triple bonded hydrogen using a drive-thru bonding structure. Meanwhile the first waldo, having fused the oxygen should place it on a bonder plate allowing the other waldo (carrying the N2) to drive-by bond it on. Sounds simple, doesn't it?
Here is my design.
The red waldo is the first to act, snatching up a nitrogen. After it fuses, it calls a β input which is really for the blue waldo's benefit.