You can see who upvotes a user's question on musing.io using the steem blockchain. Let's say I upvote this question (which I have) posed by @verbose-jimmy on musing.io:

https://musing.io/q/verbose-jimmy/f3jece4sx?r=answer

I go to find the user @verbose-jimmy on steemd.com:

https://steemd.com/@verbose-jimmy

From the musing.io link anybody who upvotes the question by verbose-jimmy/f3jece4sx will be shown as:

(steemit username) upvote @verbose-jimmy/f3jece4sx. 

Using the "find on page" option for the internet browser search for "verbose-jimmy/f3jece4sx". In this example what gets shown is:

holovision upvote @verbose-jimmy/f3jece4sx

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