Sorry for the delay in answering (circumstances have prevented me from answering forum posts for longer than we would prefer). If you are still looking for an answer here then I have some information for you.
We have a direct frequency measurement in our PicoScope 6 & 7 software, but it isn't a Driver function, and there is no frequency measurement function that is part of our example code on Github. You would have to create this yourself, but it should be quite straightforward to do is you want to measure the frequency of a single repetitive waveform. You just need to find a unique rising or falling edge in the waveform, where you can locate 2 points (A and B) on the edge, that are separated by significantly more than the peak-to-peak level of any noise in the waveform. Then you just count the number of transitions in the same direction between the points A to B, measure the time between the first a and that last A, in seconds, and then divide the number of A to B edges minus 1, by the time between the first and last A.
Regarding an FFT, again you won't find this as Driver function, or user function within our SDK, but there are a number of SDK environments that have FFT's within Libraries for that environment, e.g. Matlab, Python, C++, C#, Excel or VBA. These are generally available or need to be purchased in a specialised library (such as a Maths Library).