Magister = nominative, singular -- must be the subject.
officiorum = genitive plural, clearly connected to magister ~~> master of ceremonies??
haec = these (these what?)
alteri puero = dative singular -- to another boy
dabat = 3rd person singular verb in imperfect tense.
You really need to present this in context, in its whole paragraph, at least. In isolation like this, it's hard to tell what "haec" means or who "alter puer" is.
The master of ceremonies was giving these to another boy.