My brother in law and I were having a discussion around 'dare' vs. 'etw. wagen'. I had said something along the lines of "ich wage dich etw. zu machen" and he intimated that it doesn't really work in German. Is there a viable alternative?
Your brother is right - "to dare" has (at least) two different translations in German that each cannot be replaced by the other:
"Ich wage etwas (zu tun)" only works if I, the subject, am the one who is challenged to do something, i.e. "I dare to do something".
On the other hand, if I say "I dare you to do something", the challenge goes to you, the object. In this case, the correct translation is "Ich fordere dich heraus, etwas zu tun".
("Ich wage dich, etwas zu tun" is plain wrong and "Ich fordere heraus, etwas zu tun" is a bit weird and has a completely different meaning anyways)
It's surely possible to translate "Go on, I dare you" very literally by "Mach weiter, ich fordere dich dazu heraus", and this would be a correct German sentence. However, it does sound very unnatural (it doesn't really capture the threatening undertone of the English counterpart).
Laurin's "[Komm schon / Na los], trau dich (doch)!" (~"Come on, dare to do it!") is a much closer alternative.
The German word wagen is no complete equivalent of to dare. Merriam-Webster lists several meanings. Not all can be translated by means of wagen:
(auxiliary verb) to be sufficiently courageous to
"no one dared say a word": "niemand wagte es ein Wort zu sagen"
(intransitive verb) to have sufficient courage
"try it if you dare": "Versuchs nur, wenn du es wagst!" (: "... wenn du dich traust!")
to challenge to perform an action especially as a proof of courage or to confront boldly
"dared him to jump": No direct translation! (alternative: zu etw. herausfordern)
"dared the anger of his family": No direct translation! (alternative: riskieren)
to have the courage to contend against, venture, or try
"the actress dared a new interpretation of the classic role": "Die Darstellerin wagte eine Neuinterpration der klassischen Rolle"
P.S.: I forgot to propose an alternative. "Mach schon! Du traust dich doch eh nicht!" is a provocative way to express a challenge.