"What do you think of"
Translation:Beth dych chi'n feddwl o
Hmm. I understand what you mean with "Beth dych chi'n ei feddwl o" but that is not really the sentence given here. This is a sentence fragment where 'o' is a preposition, not a pronoun. So isn't it really a fragment of some hypothetical full sentence like "Beth dych chi'n meddwl o Dewi Lingo?"
But thinking about it further now I am confused. I read "What do you think of" as a sentence fragment. But perhaps it is indeed meant to be a complete sentence meaning "What are you thinking about?" If that's what is meant, I think the English translation here is a little awkward.