As of pip 1.3, there is a pip show command.
$ pip show Jinja2
---
Name: Jinja2
Version: 2.7.3
Location: /path/to/virtualenv/lib/python2.7/site-packages
Requires: markupsafe
In older versions, pip freeze and grep should do the job nicely.
$ pip freeze | grep Jinja2
Jinja2==2.7.3