You gain 5 life.
When a spell or ability an opponent controls causes you to discard Mangara's Blessing, you gain 2 life, and you return Mangara's Blessing from your graveyard to your hand at the beginning of the next end step.
The 2 life from having it discarded is gained when the triggered ability resolves, not at end of turn. Only the return to hand is done at end of turn.
The Mangara’s Blessing card is only returned if it is still in the graveyard at end of turn and never left the graveyard in the meantime.