How to prove episodes of academic misconduct? My former PhD supervisor asked me different times to produce false results, including complete fabrication from scratch of otherwise non-existent results. I always managed to get away from that and I have never published nor submitted anything falsified. However, I still think that this must be reported, partially because he may do that again with other students. Also, the other coauthors (including professors) have never known about this.
Unfortunately, I have no written proof of his behavior, not even email, as he has always asked me in person.
How can I proceed in such a situation?
If a professor wants to falsify data now, the professor probably falsified data in the past.  Look through previous publications by that professor for data that is obviously falsified.
Plagiarized images are the most commonly detected form of fabrication.  Not all image reuse is falsified data, but if two publications present the same image data as if they were recorded separately, this is proof of falsification.
People who falsify data are likely to engage in other academic misconduct, such as plagiarism.