Here are a few options that could point you in the right directions.
(index=netfw message_tag=RT_FLOW_SESSION_DENY) OR (index="netdhcp" ip=*)| lookup emotet_ip.csv lookup_ip AS dest| search rule=emotetc2block OR index="netdhcp" |eval dest=coalesce(dest,ip)
| stats count,values(nt_host) AS nt_host by dest src_ip
| sort -count
OR
(index=netfw message_tag=RT_FLOW_SESSION_DENY) OR (index="netdhcp" ip=*) |eval dest=coalesce(dest,ip)
| stats count,values(nt_host) AS nt_host,values(src_ip) AS src_ip by dest|mvexpand src_ip| lookup emotet_ip.csv lookup_ip AS dest| search rule="emotetc2block"
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