Which article does zimmer has eine or einen or einem?

The article "eine," "einen," or "einem" that accompanies "Zimmer" depends on the grammatical case being used. "Zimmer" is a neuter noun, so in the nominative case, it would be "ein Zimmer." In the accusative case, it remains "ein Zimmer," and in the dative case, it would be "einem Zimmer." "Einen" is used with masculine nouns in the accusative case, so it does not apply to "Zimmer."