If my Empowered Nasus, Ascended equip Song, how many points will he have when Conquer?

3 points.

Here's the breakdown:

1. 1 point from the base Conquer action (gaining control of the battlefield).
2. +1 point from Nasus's own Empowered ability ("When I conquer, you score 1 point").
3. +1 point from the Svellsongur copy — because Svellsongur copies Nasus's printed text to its Effect Text, and per Rule 718.3, that Effect Text is appended to Nasus's Rules Text. So Nasus effectively has two separate instances of "When I conquer, you score 1 point" on his rules text, both of which trigger when he conquers (since he's already Empowered, both see the condition satisfied).

This matches the precedent set in FAQ #11631 (Blue Sentinel + Svellsongur): Svellsongur creates a duplicate of the unit's text, both copies are active simultaneously, and they trigger independently.