Hard to say, perhaps a mulberry or some kind of poplar.

Yes, it is an apple. Was it bought from a reputable source? Could it have been a random seedling?

I don't see the graft???

@cecily 7A, maybe it was mislabled. If it’s a full size apple tree would it take over 10 years to produce?

It might if it’s a seedling. If it was a cultivar it would normally have been named when you bought it, not just labelled ’apple’. I’ll repeat the question, ”was it bought from a reputable source?” If it wasn’t it could be anything.

They don’t remember where they bought it.

Should they go ahead and replace it?

Nobody can decide that for you. It looks as if there is plenty of space so why not just leave it and buy a named apple from a reputable source and plant it elsewhere?