How do I assess my surgeon’s experience?

Ask him.

I would look him up online. Not sure about US, but many German doctors have their work profiles on job-related website. Besides, you can search medical journals and studies that your surgeon might write or might participate. I usually just type the doctors’ names, their specialties, and the hospital. There are many links popped up, and I just go from there.

Both good suggestions, above.
But do you have doubts about your surgeon?? And/or about the procedure??
Maybe address those with the surgeon. It's literally your life on the line, potentially. So all questions are valid.

Real simple. Ask him. If he has a problem with that, move on.

@prettypass2000 Also in Germany, there is a reputable medical website called Focus Medizin. They assigned gold and silver plague to the doctors, practices, and hospitals. I also look up the doctor on there. You can see their scores on medical studies & journals, medical services, patient recommendation, and other doctors' recommendation. I hope there is one in US too.

Besides just asking your surgeon directly, Intuitive, maker of the Da Vinci robot, has a physician locator feature on its website. Most (all?) RARPs are performed with some version of the Da Vinci robot, but not all surgeons are listed on the site.
https://www.intuitive.com/en-us/physician-locator

Ask him directly - it is normal thing ! I asked every singe surgeon that ever needed to do anything or any of my family members and none even flinched and was happy to share his/her expertise. IF your surgeon starts talking about "general results" - he is avoiding the answer and find another one. Yes, some online "reviews" can give you some insight but they can be bias and not represent real picture. Urologist that has big practice can have "4 stars" but be a mediocre surgeon since THAT part is not evaluated separately.

Find a surgeon in a big medical center that specializes in urogenital cancers and ask him what are his results - what % of HIS patients ends up with incontinence and ED, ad what effects those results.

Yes, good to ask specific questions as noted above.
Another 'questions' that occurred to me that could show the prospective surgeon's depth of knowledge/experience.
Ask about "unique" situations they've encountered.
Ask if you are somehow unique.
Ask what, if anything, is unique in your case (their diagnosis/opinion). Know that we're all unique in some way. Their reply should reflect some interesting experience.
Ask what is their hoped for result, in detail, of their proposed approach.
The best surgeon/s I've found all had these specific comments or answers.
And be creative to find out if this doctor can be enthusiastic about treating you and your specific situation.
And it wouldn't hurt to pray as you so choose.

Just ask him. I ask my surgeon and he has done over 900 with the divinci. If he would have said you will be number 4 I would have been leery. March 3 for me. Prayers for you also.

Thank you all - my surgeon is with Mayo so I'm confident in the facility. I did speak with him and he shared everything I asked about and more. My surgery is scheduled for March 4.