What is the spanish version of the name keenan?

There isn't one. It's an Irish name. The only names that would have translations across languages are Biblical names. Though 'Smith' in English translates as 'Schmidt' in German.

It's probably the same, but pronounced differently. For example, the singer Sheena Easton I heard referred to on Spanish radio as: Shay--AY-nah AY-ahs-tonn.

By which light 'Keenan' would (incorrectly, of course) pronounced kay-ay-NAN.

To get the approximate sound of the English pronunciation of the name, you write it 'kinan' in Spanish, with an acute accent over the 'i'.