apt-cache show libapache2-mod-foobar | grep Version
$ strings /usr/lib/apache2/modules/mod_pagespeed.so \ | grep "mod_pagespeed/[0-9]\.[0-9]"mod_pagespeed/w.x.y.z
Find more at http://thinkinginsoftware.blogspot.com/2015/10/find-out-apache-module-version.html
Did you try this?
apt-cache policy libapache2-mod-foobar