Normally when reviewing merge commits, we do
git diff-tree --cc <commit>
git show <commit>
git show <merge_commit>
Edit: what I'm after is to view just the hunks that were conflicted (thus not auto-merged).
Not the answer you were looking for: this is not possible with
git does not keep track of how a merge was resolved in any way or fashion. You would need something like a "4-way diff" (A, B, common parent and merge result), which I never heard of.
In theory, you could go back and write yourself a program that re-does the original 3-way merge to produce the intermediate file (with the conflict markers) and diff that to the merge result.
git has no provisions to do that for you though.