How to ask "if" and "why" in Japanese?

Question:

For example, I ask "If you don't like horror movies, why do you watch them?", or "If you're sick, why did you come to school?"

Answer:

"if" and "why" are technically translated "MOSHI" & "NAZE/DOUSHITE" (edited)
but for your sentences, I would translate (to meke them sound natural Japanese):

"If you don't like horror movies, why do you watch them?"
ホラームービーが嫌いなのに、どうして見るの？horror movie ga kirai nanoni, doushite miruno?

"If you're sick, why did you come to school?"
具合が悪いのに、どうして学校に来たの？ guai ga warui noni, doushite gakkou ni kitano?