"Do you know which instrument this is?"
Translation:Weet jij welk instrument dit is?
No, it isn't. The verb "kennen" really means to be acquainted with or to be familiar with. The direct object is always a noun (or a proper name). On the other hand, "weten" can be used with a subclause (like "which instrument this is") and is more used in the sense of to be aware of something or to be certain of something.