How do I make sub-menu links remain open using cookies after navigating to the page that the link points to?
KTMenu does not support menu expand/collapse state storing in Cookie. Basically, this is the controller by server-side code based on the cookie variable of the menu submenu section based on its unique ID attribute. You will need to add an event handler for the menu sub toggle and store the state in the cookie and in the server side, you can access the cookie value and make the menu sub shown/hidden by adding the required HTML class and attribute. You can refer to the KTMenu docs to have programmatic control based on your requirements.