You can see this か as a means to turn a verb phrase into a noun phrase. For example, the verb phrase 彼が来る can’t be used as it is as an object of a verb. You need to turn it into a noun phrase and that’s where か comes in. 彼が来るか（が ／ は）わかりません。 The particle you would expect to go with the verb, in this case either が or は, can be and often is ...
