How can I see my pending tasks of all SharePoint sites?

What kind of group is it?  A SharePoint group?  This should definitely work.

Have you got the work management service configured? If so, then MySites should also do this for you.

Yes, all the groups are SharePoint groups.

Here is a screen where you can see how I configured the web part.

Thanks, but I have no access to the work management service.

http://help.nintex.com/en-US/nintex2013/help/#Workflow/RootCategory/SharePoint/Nintex.Workflow.ItemsPendingApproval.htm%3FTocPath%3DWorkflow%7CWorkflow%2520Interaction%2520with%2520SharePoint%7C_____9

now I have read that I am thinking it may only display tasks assigned to a user (not a group).  let me do some testing.

If the task is set to create individual tasks for each recipient, would that help it?

yeah I just did a test and when assigned to a group you are a member of it won't show.  you will need to tick the assign individual tasks option on the flexi task to get it to display:

ha just seen this after I replied!

Thanks! I'll try this.

Let us know how you resolve this and if an answer exists on here, please mark as such. 

Thanks