getActiveId() can be used to find out the User ID of the user being chatted with.

The API

The getActiveId() function will return an integer data. If the data returned is 0 then the user is currently not chatting with anyone.

var chatters_userid = jqcc.cometchat.getActiveId();

Sample Code

jqcc(document).ready(function() {
    alert(jqcc.cometchat.getActiveId());
})