TL;DR
If you want to show the name of the latest tag, use:
git for-each-ref --sort=-taggerdate --count=1 --format '%(tag)' refs/tags
Some background
The command git for-each-ref is pretty useful if you want to find something in a number of commits (or tags in this case). It allows you to use variations of output and sorting methods. For example:
Show all tags including the message
git for-each-ref --format '%(refname) %(contents:subject)' refs/tags
(this is btw. very similar to git tag -n1)
Show all tags sorted by date, oldest first
git for-each-ref --sort=taggerdate --format '%(refname)' refs/tags
Show all tags sorted by date, newest first
git for-each-ref --sort=-taggerdate --format '%(refname)' refs/tags
Show latest two tags
git for-each-ref --count=2 --sort=-taggerdate --format '%(refname)' refs/tags
Show latest tag with its non-ambiguous short name
git for-each-ref --sort=-taggerdate --count=1 --format '%(refname:short)' refs/tags
Show latest tag
git for-each-ref --count=1 --sort=-taggerdate --format '%(tag)' refs/tags
(note: this is the same as the previous one, but uses the tag field)