>After FFT I would like to get ALL frequencies which are above a specified threshold.
This is in contradiction with your title. The title says you want all peaks, here you're saying you want all frequencies above a maximum. This is a totally different problem.
I'm not being picky here, peak detection is tricky and starts with a good definition of the what you require.
>I am already using peak detector but I only get 1 value as a result. But I would like to get all frequencies which are above the threshold. I attached a screen.
To get all frequencies above a threshold, simply do a compare (x>y) between the frequencies and the threshold. You'll get an array of Booleans. Put them through a for loop, and output the loop counter as a conditional array. Then you'll have all the frequency indices above the threshold.
In short, how can I use the peak detector function to get multiple peaks from FFT data, instead of just one (which is always the first one above the threshold).
Try (NI_AAL_SigProc.lvlib) Peak Detector.vi (quick drop: "Peak").