The restaurant (where/which) he has been to has been sold.
The amusement park (where/which) I like to go to is the most popular in the country.
Which one is correct?
Which identifies the one being referred to. Where means the same as at which or to which.
"The amusement park where I like to go or which I like to go to"
However, you can't really say "The restaurant where he has been" because it sounds as though he has been staying there. You could say "where he has eaten" instead.