you need a mib file.
a mib file contains the description of the numbers used in the SNMP paths.
You can try to install a MIB browser like iReasoning MIB Browser and then do a tree walk from .1 to see the entire tree.
Then you can cahnge a few PoE ports and make the same tree walk to discover changes.
Problem is that it can be a huge tree on some devices and there might also be a lot of changes, so a mib file is just easier.
The MIB browser can load the mib file and use it to find the right path where you can then copy the number path from for use in the SNMP sensor in HA,