So ive been trying to figure this out for the past week.
All of the passive NB Assassination abilities state in CAPS:
"WHILE USING ASSASSINATION ABILITIES"
which seems pretty clear. The passives will work if you are using an assassination ability, not any other time.
So then I look at the first passive: Master Assassin
Which states that it increases "Weapon Damage" for attacks while stealthed or invisible.
Here is where the confusion sets in. First, typically class abilities DONT use weapon damage. They completely ignore it. In this case, all of the abilities in the assassination tree use spellpower/magicka for their damage. Not weapon damage.
So how exactly is the passive "Master Assassin" going to help you at all "while using assassination abilities" such as the first ability "Assassins Blade", when bonus weapon damage (from the passive) is completely ignored by that ability?
Likewise, what good is getting a bonus to weapon damage going to do for weapon attacks, if it ONLY works "while using assassination abilities" Light attack? Strong attack? Any weapon skill? Nope...not an assassination ability, which means no bonus damage (according to the tooltip description).
The skill, based on its descriptive info, completely contradicts itself, if its accurate, making it a 100% useless skill. It will never provide ANY bonus to ANY attack.
Would be nice to have the devs clarify how this works, or simply, fix the tooltip so that it states the REAL info. (or maybe the skill needs to be fixed all together)