"Are there clocks?"
I don't know if any nouns absolutely need the お. But there are several which customarily take it (おすし、おてあらい、おべんと). Actually, おちゃ seems to only sound right with the お. I think it's one of those things in language that is best learned through practice by listening to other speakers. Eventually, you develop a "feel" for when certain nuances sound right in the context. In the meantime, you won't be wrong by leaving the お off of every noun.
If your question is about が vs は, I think both are ok.
If your question is about あるか, it's probably wrong.
ありますか is of course correct, but I doubt あるか is.
It should be ある? instead. Or あるの？
According to https://jref.com/articles/interrogative-forms.118/ the か is hardly ever used with the neutral form.
Another source : http://www.guidetojapanese.org/learn/grammar/question#The_question_marker_in_casual_speech
When you are just asking about the existence of something, asking in the positive or negative has about the same nuance as in English. "Are there clocks?" vs. "Aren't there (any) clocks?" However, when making an offer to someone, offering in the negative is slightly more polite and sounds more like an offer. ケーキたべますか？Will you eat (some) cake? vs. けーきたべませんか？Won't you eat (some) cake?