Lucy‘s bike is broken.对broken提问,可以说成what happens to Lucy’s b

should be:
"what has happened to lucy's bike?" (if you want to stick with 'happened')
in present perfect tense
if you use 'what's wrong with"/"what's the matter with", the question would be:
what's wrong with Lucy's bike?
or
what's the matter with Lucy's bike?
三个其实都对!=]