how to access database created with dbforge

1. If a database is created using dbforge, can you use query builder for the dynamic database(insert, update, delete)?  

In a word, yes.

3. How do you "select" the dbforge created database to preform queries on? ("$this->db->query('use db2');" so, this is the 'use' statement and it works the same as in SQL syntax?)

Consult the documentation on Database Configuration. Down that page a way it describes how you can store multiple sets of connection values. If your dbforge database connection is stored like this

PHP Code:

$db['forged'] = array( 
        dsn'   => '',
        'hostname' => 'localhost',
        etc...
); 


That database could be loaded like this.

PHP Code:

$this->load->database('forged'); 


After which you simply use

PHP Code:

$this->db->query_builder_methods_here(); 


The Connecting to Your Database documentation is helpful too.