I ran across this issue and adding jdk to eclipse.ini did not solve this problem.
Eclipse tries to resolve jconsole.jar by following path relative to eclipse jre path
/../lib/jconsole.jar
Eclipse default JRE must point to JRE inside of JDK folder, so it can resolve jconsole.jar.
In my case my JRE eclipse was pointing to
C:\Program Files\Java\jre1.8.0_20
Correct should have been
C:\Program Files\Java\jdk1.8.0_20\jre