1. please teach me the skill build for rena which should choose to power up on the skill tree thanks.
Class ? Lvl ? Pve or pvp ? If you are asking class then Ga is strongest atm followed by Nw and the Ws.
9.) Spinning Crescent - Good damage vs groups, and multi-hit for locking things down.
10.) Tie between Assault Kick [light] and Crescent Kick [critical] - The critical trait on Crescent makes it good for high defense monsters and bosses, but the damage/mp on assault kick is quite surprisingly high on a single target. It's really your choice which is better.
If A-Slot only, do Airelinna (on all the time), Violent Attack (bossing and groups), Phoenix Strike (field clear), Dive Bombing Kick (bossing), and Siege (all purpose) in my opinion. This will give you a wide range of options for defense and decent damage. I tested all of these vs monsters in training and in dungeon.
^Looks good, I recommend Max Pain instead of Low in my opinion because of the insane dmg on that active.