"He is one of the people that have achieved sucess." Is it correct? It takes plural verb, right?
It does take a plural verb, and when you change the spelling to success, it will be correct. However, it sounds a bit odd to me as countless millions of people have been successful. I would use one of for something more exceptional.
I think it is grammatical if the question mark is put after the closing quotation mark, but I would simply say 'He is a successful person'.
Is it correct to say "He is among the people who have achieved success?"
I got called out on that. Apparently, a question mark goes inside the quotation mark.
In British English, we are happy to put any punctuation outside the quote if it isn't part of the text.