Q: raw format for PANASONIC DMC-FZ100?

Yes it is - see Digital camera RAW formats supported by OS X El Capitan - Apple Support

What is the problem? What exactly happens?

LN

Yes, the camera is supported in OS X 10.11. or newer.

See the list:   Digital camera RAW formats supported by OS X El Capitan - Apple Support

What happens, when you try to edit?

Does Photos show the RAW files as unsupported?

Can Panasonic's Silkypix open the RAW files?

Exactly how did you import them? Have you done any clean up on your system or run any cleaning software on it?

Do you have a manager library (the Photos preference to copy imported items is checked - the default) or a referenced library (you unchecked this option)

LN

I got a big triangle with an admiration sign on it. Nothing else

The RAW originals may be missing from the library. Can you export them with as original files?  Select a few of your RAW images and use  "File > Export > Export original files" . DO you get an error message?

The triangle with the exclamation mark can mean two different thing -

1. that the original image files are  missing from your Photos Library or cannot be accessed because of a library corruption or permission problem
2. or that the format is not supported.

Trying to export will test if the problem is 1. or 2.  If you cannot export the originals, Photos cannot find your images.

But I still do not know, if you can export a photos from Photos using   "File > Export > Export original files" . Do you get an error message or not?

We really need to know if the RAW files are in your Photos library or have been removed somehow.

Try if reinstalling the last RAW support will help. 

Download the installer from the support page, not the AppStore:   https://support.apple.com/kb/DL1874?viewlocale=en_US&locale=en_US

Then try again.

If that does not help, reinstall the System. Install by booting into recovery in top of the current system. See:  OS X: About OS X Recovery