Oracle - PFILE or SPFILE when instance is down
It does not really matter, but spfile is favored because it provides better functionality.
When an instance is down, it does not use any of them.
You may check the alert log for the previous startups, the pfile/spfile location is displayed there after each startup.
If the database is registered in Grid Infrastructure as a database resource, the spfile location is typically (but not mandatorily) specified there (srvctl config database -d database_name).
By the way, most databases use SPFILE.