Yes, it's technically possible, but since the object being dislocated is a clause instead of a single word, it's much more jarring and potentially confusing. This is probably something a learner should avoid.
If you spoke this sentence, you would need to pay close attention to your tone and emphasis, stressing "When" by raising the pitch of your voice, inserting a very slight pause before "I" and then lightly stressing "know" (not as stressed as "when"). In writing, you might need to put "When" in italics and even to insert a comma after "come" to demarcate the clauses. These measures help the listener/ reader correctly parse the sentence since the word order is not the usual one.