This should work to enable all traps on a 2950 running recent code:
snmp-server group v3tgrp v3 notify v1default
snmp-server user tuser v3tgrp v3 auth md5 cisco
snmp-server enable traps
snmp-server host 1.1.1.1 traps version 3 auth tuser
After entering these commands, show snmp should look like:
...
SNMP logging: enabled
Logging to 1.1.1.1.162, 0/10, 3 sent, 0 dropped.
SNMP agent enabled
You should also see a list of specific traps enabled in the config. If, after entering these commands, traps are still not working, please post the show snmp and complete show run. If you cannot share that information on an open forum, then please open a TAC service request with the same information.