There are several options to do that:
1. You can check SNMP agent configuration manually by analyzing config
file etc.
2. Refer to SNMP agent documentation
3. Automatically

I'm not going to talk about options 1 and 2. The automatic approach is
based on some preliminary assumptions that you have to make in order to
query agent:

You need to specify read community string for SNMPv1, SNMPv2C. If you
have no idea about community string you can just simply try something
like public, private, etc. These are defaults.

SNMPv3 is more complex due to User Security Model (USM). I would use
noAuthNoPriv security level, so you don't have to specify
authentication and privacy keys (passwords). Try to use "initial" as
the username. The rest of parameters like context engine id, context
name you can leave blank. This information is going to be retrieved
automatically during initial request.

Hope this helps,

Sincerely,
NetMechanica
http://www.netmechanica.com