。
I don't know how to cook.
Literal
Cooking [possessive-の] way-of-doing [subject-が] don't-understand.
~の仕方 is a productive pattern: attach 仕方 to a noun to mean 'how to do X.' The が marks the whole phrase 料理の仕方 as the subject of わかる (to understand). わかりません is polite negative — the speaker doesn't know the method.