Can we send the assigned pending workflow tasks reminder email notifications to the assigned user

There's some functionality you can do with setting Deadlines on the tasks. See: https://support.ptc.com/help/windchill/r13.1.0.0/en/index.html#page/Windchill_Help_Center/workflow/WFTabProcessPropDeadline.html

It doesn't send repeating emails though. 

Doable for sure. I’ve done it. In my case we sent a reminder if 5 days past since the task was assigned. If the task still wasn’t done after 5 days we sent another reminder.

Think loop. Simple programming solution.