After PSMI-I whats next PSM-II or PSK-I

It totally depends on what you want to achieve.... Your personal goals... Whats your affinity with Kanban? Where do you want to be in the next few years?

PSM-II is a major achievement to have btw in any regard

Why do you want the PSK? Are your teams utilizing any parts of Kanban? 

Personally, I think the next step should be the PSPO. Learning more about the PO role and earning that cert has helped open my eyes and I'm growing into a better SM because I have a greater understanding of what PO's deal with and their responsibilities. 

You can't go wrong with either PSM II or PSK. Just preparing for them will help you become a better Scrum Master. If I had to pick one and only one (tough choice!), I would lean towards PSK as it is a game changer in my opinion. I feel like you could take the Kanban practices and metrics and vastly improve how your Scrum Team delivers value through better flow. You'll never want to use velocity again (if you use it today). And the nice thing is you don't have to change Scrum to add in these practices.

If it came down to taking a course, PSM II would be my pick, as you come away with so many valuable tools (and learn how to use Liberating Structures) and lessons for being a better Scrum Master, and serving your Dev Team, PO and organization.