This would be more precisely answered if this was in a complete sentence, but you could say "¿Por qué debería hacerlo?" This is really "Why should I do it?", but you normally would not leave off the verb like you might in English.
You should google English to Spanish translation.
You should learn to say it in English. In Spanish it is "Donde esta su automovil?"
It should just be "Brent."
ambos deben
No deberíamos matarlo
you should be in: deberias estar en you should be a: deberias ser
"Idiota" should work fine.idiota
debo preguntar porque?
debes creerlo
Buenos días.
they should or owed depending on how used
it should be "tonto" or "torpe"