There isn't a specific board for answering the question of the week that is asked in the 'I love Mondays!' video that is uploaded each Monday. Watch the 'I love Mondays' video to find out information on how to submit your responses.
Alternatively if you are asking about the question of the day which is displayed above the list of new topics when you click the Forums tab. Simply click the yellow text of the question and you will be redirected to a page displaying user's response to the question and in the top left you'll see the button for answering it. Click that and you'll find a window appear allowing you to type up your own response.
Any other questions feel free to PM me and I'll gladly help you out :)