For readibility, try using IN():
index=sne host=nwbsnep* sourcetype IN(sne_CAS_elilogs,sne_CMS_elilogs) Service.Operation IN("A","B","C","D","E","F","G","H")
The issue seems to have been, though, that in your second parenthesized set of ORs, you had this:
OR "Service.Operation"="D "OR "Service.Operation"="E" OR "Service.Operation"="F"
In SPL, the OR has to be separated from what it’s or’ing by at least one space
You had one slammed against a quote mark
from User warren – Stack Overflow https://stackoverflow.com/questions/58915438/searching-for-specific-values-in-splunk-query/73129443#73129443
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