The best way to know where to start is to look for discussions on manga-focused websites. Fans often share their experiences and advice on continuing after the anime. Another option is to check social media groups dedicated to Baki Hanma to get suggestions from fellow fans.
Well, usually you can find out by researching on manga forums or asking fellow fans. Sometimes, the publishers or official websites also provide guidance on where to pick up after the anime. Another option is to look for recommendations on social media manga groups.
I'd suggest looking for the chapter that directly follows the events of the 2023 anime. Maybe check online manga forums or fan communities for specific recommendations.
You can start from the beginning of the next major story arc. Usually, there are clear indications in fan communities or online discussions about where to pick up.
Websites like KissManga and MangaPark might have what you're looking for. But be aware that the availability can vary, and sometimes you might need to search a bit to find the exact chapters you want.