I recommend to use Google Analytics to get details of different aspects of your users behaviour on your site.
But if you only want to log requests for specific pages/methods on your site you could create a method to insert data into a database table every time any method gets requested:
private function _log_activity($page='default_page'){
$user_ip = $this->getUserIP();
$sql = "INSERT INTO log_table (user_ip, page, request_date)
VALUES($user_ip, $page, NOW())";
$this->db->query($sql);
}
Copy the method getUserIP() in your controller from here: How to get Real IP from Visitor?
And usage in every method you want to track requests from:
$this->_log_activity('page_or_method_name');