Particles を - が

I know that を is an Object Marker (the action is happening to it) , and が is a Subject Marker (the doer of the action). However, it's often difficult for me to determine which is which in a simple sentence. Take these two sentences for example:

英語が話すことができますか
英語をはなしますか

In this case, is が or を the correct Particle?

Thank you,
Robert

I'm not a grammar expert but I think を would be correct in both of these example sentences.

英語を話すことができますか
英語をはなしますか

が can be the object marker of the potential form of a verb, so が can be used for 話せる.

×英語が話すことができますか
〇英語を話すことができますか
〇英語が話せますか
〇英語を話せますか

Incidentally, が in 英語を話すことができますか is exactly for this usage. Grammatically, 英語を話すこと is interpreted as the object of できる in this sentence.