Can I retrieve data (photos/videos) from a completely shattered s9?

If you charge it and try turning it on, then hook it to the computer. It should recognize it and ask if you want to import your pictures and videos. If you can't get that to work i would recomend contacting iPad rehab at iPadrehab.com and see if they can get your data. They usually charge 300 dollars for iPhones and guarantee it or no charge, I don't know if they do this with Samsung. I would call them if you can't get it to get the pictures off. You may just need to put a new screen on the phone so you can unlock it. You can put a new screen on it fairly easily, what a few of the videos from YouTube and follow the directions one step at a time. Get a basic set of tools and also get a magnetic parts board to keep track of all of the screws ( some screws may be different lengths so make sure that they are put back in the same place or it can damage the motherboard). If you think this is above your skill level or aren't interested check with ifixit and they can direct you to a repair shop in your area. Best of luck.

What if you put the phone into twrp and just dragged the files you need to your pc? Or you can use some broken Samsung recovery tool.