It have gotten it to work but not to create a custom data tip function. Ii also looks like you are passing it the axes handle not the figure handle. The below code works but when I click my axes to get a custom data tip using myupdatefcn I get "Unable to Update data tip using custom update function".
dcm_obj=datacursormode(app.figHandle);
dcm_obj.Enable='On';
dcm_obj.UpdateFcn=@myupdatefcn;
