find difference between 2 remote branches

What you are looking for is probably something like:

gitk --left-right remotes/branch-V4.4...remotes/branch-V4.2

or if gitk is not available:

git log --oneline --graph --decorate --left-right --boundary --date-order remotes/branch-V4.4...remotes/branch-V4.2

You might also want to try it without the --date-order, but especially in complicated situations, I found that git log produces more useful graphs with that option.

Every commit in that graph will be either marked with <, > or o - that means that they are part of the left branch, the right branch or a “boundary commit”.

Use git log instead of git diff:

git log remotes/branch-V4.4..remotes/branch-V4.2