Simple Q&A D&D 3.5 (by RAW) XXI

[Curmudgeon]

A 1099 Yes.

A 1100 Just once.

Fell Drain says

You can alter a spell that deals damage to foes so that any living creature that is dealt damage also gains a negative level.

The metamagic alteration of any spell is limited to a single negative level to any living creature.

A 1101

You (the PC) are the spellcaster, not the familiar; the spell uses your caster level and attribute. As an NPC, the DM decides what actions the familiar takes with any shared spell, but the spell's characteristics are set at casting. Note regarding the above answer that an enemy cannot gain a further negative level from the combination of Cloud of Knives delivered by both spellcaster and familiar.

A 1102 No.

A knife may only be launched at the beginning of your turn. Since you already have performed some other action (casting), it is no longer the beginning of your turn.

A 1103 Maybe.

All effects with a duration of rounds begin from the time they are initiated and end immediately before the character's turn (at the same initiative count) in a subsequent round. This means that the staggered condition's "each round" limit in this case is not based on the entirety of the enemy's turn in this cycle of the game clock, but a round spanning portions of two game cycle rounds. The enemy retains their game cycle limit of actions in a round, and gains a new limit from being staggered partway through their turn. If they have already taken a move action and your AoO interrupts their standard action, they are limited starting from that point until their next turn, and can still take a standard action; effectively, nothing happens. If instead your AoO interrupts a full-round action the staggered condition would prevent that from being resumed.

A 1106

Your patron is the deity you worship.