"Whose is Samsung?" Is this sentence grammatically correct?

Both versions are grammatically correct. From context, they both may be easily understood, but even with no context, they are still grammatically correct.

Those who are naysayers, please point out any error in grammar.

Both of your ideas feel wrong to me. In Britain I would say "Who does Samsung belong to?", or "Which company owns Samsung".

Well, Samsung is a large, publicly-traded Korean company, so it's owned by a lot of stockholders.

You could say 'Sony is Japan's company. Whose is Samsung?' That would not be perfectly correct, but it's the way we speak.

Otherwise you'd say 'Whose company is Samsung?' or 'Who is Samsung?'

No.