Ok thank you. In this document it says :
and when received by snmptrapd is displayed as follows

1999-11-12 23:26:07 localhost [127.0.0.1] TRAP-TEST-MIB::demotraps:
Enterprise Specific Trap (demo-trap) Uptime: 1 day, 5:34:06
SNMPv2-MIB::sysLocation.0 = "Just here"
But where is it displayed ? In a file ? Which file ? Where is it lockated ?
Many thanks.