If I understood you correctly you are asking where the excutables for your 630 nagios checks are located, right?
Basically they can be anywhere on the checkmk server, but usually they are located in either ~/local/lib/nagios/plugins or ~/lib/nagios/plugins within the site directory. If not, the Command line field of the rule must contain the full path. The online help of the rule says:
If in doubt, you must check all your Nagios rules.