expression
most of all; extremely; supremely
Adverbial phrase emphasizing the highest degree; often used before adjectives or verbs to mean 'more than anything' or 'to the utmost'. Slightly formal or emphatic.
この上もなく幸せです。
I am supremely happy.
この上もなく重要な問題だ。
It is an extremely important issue.
Also means 'more than anything', but 何よりも is more conversational and can be used in a wider range of contexts, while この上もなく is more emphatic and formal.
A common, neutral intensifier meaning 'very' or 'extremely'. この上もなく carries a stronger sense of 'supremely' or 'above all else'.
From この上 (kono ue, 'above this') + も (mo, 'even') + なく (naku, adverbial form of ない 'not'), literally 'not even above this', i.e., 'nothing surpasses this'.