Use Brady's Reagent (2,4-DNPH) to test for the presence of the C=O bond in a carbonyl compound. The formation of a yellow precipitate indicates a positive test result. Then determine the melting point of the product to identify the original carbonyl.
Alternatively you can use Tollen's reagent to determine whether a carbonyl is a ketone or an aldehyde. As Tollen's is a (weak) oxidising agent, there will be no reaction upon addition to a ketone, but a silver precipitate will form with an aldehyde.