1) Open up users.conf and add the "qualify" setting to the proper trunk context. For more information on qualify see
http://www.voip-info.org/wiki/view/Asterisk+iax+qualify . Note that this is used primarily to monitor the responsiveness.
2) Options > Advanced Options > Show Advanced Options. After doing this Asterisk Logs will be visible in the left-hand menu.
3) Whether or not a trunk registers
should be visible on the System Status page - if this isn't the case you might need to ask your provider if they can provide any assistance.