Hi Sandrine
Good question:-
There's article providing general guidance and requirements around the K2 tasks that need to be completed when migrating a K2 integrated SharePoint 2013 environment to SharePoint 2016. It includes high level steps for migrating the SharePoint environment in order to provide context around when K2 specific tasks need to be completed.
Please to refer to this documentation for that https://help.k2.com/products/kbs100229
Should you find this information useful kindly mark it as "Solution and/or Kudo", as this will help others in the future.
Thank you
Widson.
pK2 will not accept any liability for any issues arising from actions taken in respect of the information provided by any forum member]