Hmm... that the point of the VPN.
If a user on your premises establishes a VPN from his PC to a remote site, the tunnel is between his PC and the security device at the remote site.
You should not be able to see what is in that tunnel, as it defeats the whole point of securing it.
If, instead, you setup a VPN between your firewall and the remote site and allow your user access to the remote resources, you should be able to monitor the content of the traffic before it is encrypted by the Check Point.