Ah sorry, this thread started as an inquiry about tracking conversions from Facebook ads, and you didn't mention otherwise, so that's what we thought you were trying to accomplish.
The only way of tracking cart button clicks that we support would be via Google Analytics, if you use our version of the GA tracking code (see http://www.e-junkie.com/ej/help.tracking.htm), but this probably would not be relevant to tracking clicks in association with Facebook ads.
In theory, it may be possible to replace the standard onClick= JS call in our cart button codes with a custom call to some function that tracks the click and then calls our standard function that adds the item to cart -- or even leave the onClick= event as-is and have your custom tracking JS recognize clicks on elements with class="ec_ejc_thkbx" -- but providing more specific instructions to accomplish that is beyond the scope of support we can provide. The Developer Directory link at the top of our site lists competent, E-junkie-experienced developers available for hire to perform custom work.