<PerkTreePosY>3</PerkTreePosY> " I don't know what this does for the trait? "
When an <abilitybonus> has the tag <AbilityBonusType>Unit_Level</AbilityBonusType>, that means it is an ability to be included in a champion path trait tree. The X and y position are a zero-indexed (starts at 0) coordinate location on the tree.
<StrVal>UnitStat_Defense_Pierce</StrVal> " Is pierce the only defense? or can i make it cutting? "
For LH, physical damage is Defense_pierce and Attack_pierce. Don't try to mess with that until you have more modding experience. It's a carry-over from Fallen Enchantress and you'd have to adjust all the weapons and armor back to the way it was (or copy old files from FE and modify them).
<Attribute>Dodge2</Attribute> " Attribute Dodge2 not sure what this is or where i can find a list of attributes. "
Dodge2 is inside a <PreReq> parent tag, meaning you need the Dodge2 ability from the tree before this ability (in which this is wrapped) can be selected. This tag is along with x,y coordinates are primarily how the ability tree is built (the pre-req tags incites the lines between abilities to appear).