Learn Turkish: Brifing için beklenen organizatör burada mı? - Is the organizer expected for the briefing here?

It is formed from the verb stem bekle- (to wait/expect) + the passive suffix -n + the subject relative participle -en (who/which/that). While the active form bekleyen means 'who is waiting', the passive beklenen means 'who is expected'.

Since the organizer is the one being expected (the object of the expectation), why do we use the subject participle -An instead of the object participle -DIk?

Because of the passive suffix -n. When a verb is made passive, the original object becomes the grammatical subject of the passive verb (the organizer is the one 'who is expected'). Since the noun being described (organizatör) acts as the subject of this passive action, we use -An. If we used the active voice to say 'the organizer we expect', we would use the object participle: beklediğimiz organizatör.

Could we use the dative case brifinge instead of the postposition brifing için?

Yes, but the nuance shifts slightly. Brifing için beklenen means expected for the briefing, highlighting the purpose or reason. Brifinge beklenen would mean expected to the briefing, treating the briefing as a destination they are supposed to arrive at.

What is the effect of placing the question particle mı at the very end of this sentence?