It says it "increases the mana gained from your Spiritual Attunement ability by 10%"
So if you gained 20 mana from a heal, you will now gain 22 is my interpretation.
So it would be 0.1*1.1 = 0.11 or 11%.
But I don't have T6, so this is just what I get from my interpretation of the tooltip. Perhaps some T6 pallies could comment.
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