I want to get the final ability in the shadow skill line (not playing Atm so can't remember the name), it's takes level 42 shadow to unlock and I'm at level 35. Is there a way to grind this skill line quickly?
Put skills from that line on your bar. Whenever you gain experience from quests or kills, skills on your active bar and their associated skill lines* go up. You can also set up a specific "quest turn in bar" loaded up with skills you want to increase, and make sure that one is active when you turn in quests. That's a lot easier on PC, with the right addons.
* some skill lines don't work this way, such as Mage/ Fighter Guilds, Undaunted, Soul Magic and the Assault/ Support lines. Those all have special rules.
Snit AD Sorc Ratbag AD Warden Tank Goblins AD Stamblade
As a NB you should already be useing cloak and surprise attacks. Set the shadow ultimate as your ultimate and just eep questing/grinding. It wilk get there.
You level up class skill trees by having abilities from those trees on your active ability bar when you gain experience. If you have a shadow ability on your ability bar when you turn in a quest or kill an enemy, it will level up the shadow skill tree.
The more abilities from the tree that you have on your bar, the faster it will level.
EDIT:
Also, dont stress too much over getting the summon shade, it's not nearly as interesting or useful as you'd think.
Keep the invisibility skill on main weapon bar and use sneak attack
Edit: get sneak attack (forgot pre-morph name but it's the skill right beneath invisibility skill), imo it's much much better than shade skill. Sneak attack is a tremendous melee skill for nb's. On mobs, sneak attack will also stun for 3-5 seconds (forgot which) if used from sneak/invisible so for 2 group mobs, ambush,then invisible + sneak attack on other mob then you finish off original mob with no problem then go back to stunned mob, pretty much makes 2 group mobs single mobs