How to find sibilance sensitivity? How to find which Freq?

[SupperTime]

To calm something like a "clap" I'd suggest a compressor. It can be set to do almost nothing unless it meets one of those.
A really fast transient can contain a very large number of frequencies, spread all over the band limited signal. So an EQ might not be the right tool for that.

I have an rme adi-2 dac which has a graphical eq, I can change q, freq, gain in it but I don't know how to shelf it or how to help the claps or peaky treble
Here is how it looks like

 

[castleofargh]

If the audio source is not a computer, you can find the real thing in a box but obviously that won't be free.
If your source is a computer, then any player that lets you add a VST plug in will do. Or you could convert your track inside a DAW and then only play the version that doesn't annoy you. Just google for some free compressor VST and try. Some players might not work with VST3, and if the VST host(like an audio player) is 32bit(the coding like for an OS, not the audio bit depth), you'll usually need the 32bit version of the VST. Luckily, VST plugins tend to come with various installation versions.

I'm low level padawan with EQ, but a real noob with audio compressors. So you'll want to discuss this with someone who knows something.