@impastable and those like him.
You will find the spot that the OP mentioned somewhere in the game handler. But I would not recommend manually searching for it just a pain really. Just search for some unique word in the game, like one of the city names, some attribute, etc and it will put you within the game module, from there you should have no problem finding the mentioned spot, though you can also put the onclick in many other places as some1 already mentioned.
Anyway once you do that you put in you new attribute, in this case onclick, which as it says, sets up an event for if you click it does something, the something being what you put in for the onclick, so after you put in the onclick, you then enter the data, key note here, don't try to put in both at the same time you'll just come up with an attribute that does not exist. So make sure you enter the data after you put the attribute.
Hope this enlightens a few of ya, ciao. (broken image removed)