It's identical to the esxcli comand parameters
Something like this (I do 2 gets to see the before asnd after)
$esxcli=Get-EsxCli-VMHostesx1.local.test
$esxcli.system.snmp.get()$authentication="none"
$communities="MyCommunity"
$enable=$true
$engineid="0x12345"
$hwsrc="sensors"
$loglevel="error"
$notraps="reset"
$port=161
$privacy="none"
$remoteusers=$null
$reset=$null
$syscontact="System Contact"
$syslocation="System Location"
$targets="192.168.1.1/MyCommunity"
$users="user/-/-/none"
$v3targets=$null
$esxcli.system.snmp.set($authentication,$communities,$enable,$engineid,$hwsrc,$loglevel,$notraps,$port,$privacy,$remoteusers,$reset,$syscontact,$syslocation,$targets,$users,$v3targets)$esxcli.system.snmp.get()