Answer 1: With your transforms.conf entry to filter events are kept in Indexers and Indexers are added as search peer to your Search Heads, run this from your search head to get list of REGEXes.
| rest /services/configs/conf-transforms | search DEST_KEY=queue FORMAT=nullQueue | dedup id
To get the same info from Intermediate Forwarders, you need to add them (or one of them) as search peer to your search head (or instance from which you'd run this query).
Answer 2: This will give you a rough metrics about number of events discarded (uses the nullqueue metrics logs showing nullqueue sizes).
index=_internal sourcetype=splunkd component=Metrics group=queue name=nullqueue current_size>0 | stats sum(current_size) as Discarded_events
This should work for both Indexes are Intermediate forwarders (as long as internal logs are being forwarded to indexes).
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