For selected Event Label results are:
How to present in custom report value of CTR [%] = (Total Events for Click) / (Total Events for Hit)?
Unfortunately there is no way to perform calculations of this type within Google Analytics or Google Data Studio. You can divide one metric by another (such as Unique Events / Total Events), but not one dimension's metric value by another dimension's metric value.
If you need this on an ongoing basis, so it's worth some extra work to set up a report, you can do it in Google Sheets with the Google Analytics Add-On. The add-on documentation will get you started. Your actual report would be in a different tab of the spreadsheet, where you can copy over data directly from the GA reports and also do whatever arithmetic is useful to you.
