How to check if Index Key (Prefix) Compression is used

[SAPSupport]

We are checking Oracle's compression status, but We don't know how to check if Index Key (Prefix) Compression is being used.
Could you please tell us how to check if Index Key (Prefix) Compression is used?

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[jrapp_ch]

If you want to query the Oracle data dictionary for information about Indexes, you can use

https://www.viskey4you.com

There is a folder on the left side called "Indexes".

This tool also includes a query builder, against the dictionary