So I did a lot of testing in various skill trees in how xp gains work and have come up with the following data to share with you the forums, in the hopes that it somehow helps you, after all, knowledge is power.

Disclaimer: some skill lines require methods other then xp to level so I excluded those, also all of my percentages are slightly rounded for ease of understanding, but only rounded by about 1% so they are still accurate.

Class skill tree leveling:
-each skill (including ultimate) from a given tree gives 30% of xp gained to its given tree and stacks additively with one another. meaning if you get 100 xp and have one skill the tree gains 30 xp, if you have two skill it gains 60 xp, and so on.

Armor skill tree leveling:
-different locations of armor grant different amounts of xp gain. with the chest location granting around 20% of gained xp to its given tree and every other location granting around 10%. this all stacks additively with one another.
-the training trait only effects a given locations xp contribution and not all locations and seems to be working as advertised.

Weapon skill tree leveling:
-the weapon(s) themselves grant about 40% of gained xp to its given tree.
-individual skills grant about 30% of gained xp to its given tree. this all stacks additively with one another.
-the training trait only effects the weapons themselves contribution to xp and not the skills contribution, but the bonus is as advertised.

Racial skill leveling:
Disclaimer: I only tested the Khajiit medium armor xp bonus as I have full character slots and could not test others.
-the racial bonus claiming a 15% increase is not working as advertised. it is instead granting a 25% increase to xp gain, so its working better then advertised.

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that's all I got, if anyone has any other tips or questions or would like to do their own testing I will happily update this post, have fun

-Wing