Mention marking duty for a course in an early academic career CV I am first year post-doctoral fellow. I have been asked to carry out some marking duties by my PhD supervisor from another university which I am not currently affiliated with, but where I got my PhD from. 

Can I mention this marking duty under my teaching experience on my academic CV?
You can mention it, but there is no benefit to doing so.  Your marking and grading experience is not important to hiring decisions.