Although some readers still believe it, the rule that prohibits ending a sentence with a preposition is a myth. When the preposition is redundant, though, you should leave it out. If your readers are likely to believe that ending a sentence with a preposition is always an error, consider rephrasing to avoid it.
Where is it at?
Where is it?
That’s the building she went into.
That’s the building she entered.
It’s a terrible situation to find yourself in.
It’s a terrible situation in which to find yourself. (More formal)