Here is a base search for Splunk licensing events:
index=_internal source=*license_usage.log type="Usage" | eval indexname = if(len(idx)=0 OR isnull(idx),"(UNKNOWN)",idx) | eval sourcetypename = st | bin _time span=1d | stats values(poolsz) as poolsz sum(b) as b by _time, pool, indexname, sourcetypename | eval GB=(b/1024/1024/1024) | eval pool=(poolsz/1024/1024/1024) | fields _time, indexname, sourcetypename, GB, pool
This search will get you a list of usage across index and sourcetype for your specified timerange and is collected into 1 day buckets (since licensing goes by day). In order to get usage by index you can just add "| stats sum(GB) by indexname, _time" to the end of the search and that should give you each index's license usage for each day within your specified timerange. Unfortunately, I am not familiar with Splunk Cloud _internal events. Are these the events that aren't showing index fields within the event? If this search does not work for you, could you post a sample of the events you are seeing?
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