Are you looking for a command like
git stash list -p
This shows the diff of each stash, together with the messages you provided.
Edit: In case you know which stash number you want to show (i.e., not show the entire list but one specific stash), you can do
git stash list -p -n 1 --skip i
where i is the number of the stash you want to show. (this will show stash@{i}).
As mentioned in the manual, the git stash list command takes options for formatting similar to git log, see the git log man page
The -p option ensures that all the information you want is printed (you can play around with the formatting as explained on the git log man page)
The option -n 1 ensures that only one stash is printed, also see the git log man page
The option --skip i tells git to not print the first i stashes, hence, combined with the option n 1, only stash@{i} will be shown. Again, see the git log man page