This can be done with the following command on the ASG:
cc set awe global ap_debuglevel 1
The following values are allowed:
0 - default loglevel
1 - increase WiFi loglevel
2 - increase EAP authentication loglevel
3 - increase both loglevels
After setting a higher loglevel the APs will be reconfigured and afterwards send more log output to the ASG. The log can be found in /var/log/wireless.log on the ASG.
This will only help in narrowing down issues between wireless clients and the AP and won't help at all for connection problems between the AP and the ASG.