It can not be an apposite because it has nothing to be apposited to. For it to be subject the commas would have to be out. It looks like a vocative to me.
fIlia mea > is certainly in the nominative case and is therefore the subject of the verb > laudat> . So you have (in English) "My daughter always praises…what?. Well, since > sapientiam amIcArum > is in the accusative it is the object of the verb (it receives the action). You have been led astray by the concept of apposition. It doesn’t apply here since there is no other noun phrase in the nominative. You may be confused about the function of > laudat> . While a conjugated verb may stand alone and suggest its subject, you have an explicit subject here: > fIlia mea> .
In my not so humble opinion this is a botched phrase that only confuses the student instead of helping him learn Latin.
“laudat” is 3rd person singular present indicative active, and, if you consider “mea filia” as vocative, then it should have been “lauda”, 2nd person singular imperative.
Not necessarily. It can be a simple statement, addressing a specific person, as opposed to an order, and with an implicit subject (deduced from context).