You can't with the out of the box K2 worklist webpart.  Possible options:  http://www.k2underground.com/forums/t/13510.aspx

If this is important to you I would also recommend submitting this as a support ticket feature request so that K2 can prioritize it.  Its a fairly popular request that a lot of my customers request as well but currently can't easily be done.

Thanks for your reply, however have go thru the forums... it require customizing the web part before it could use.. it will be good if there is any tested solutions with guild on how to deploy or develop... our current environment is SharePoint 2010

Hi Kalvin, did you resolve this question? Looking do supress the options on K2 worklist items also.

Try writing your own web part and retrieve the data via the work list service broker?

http://www.k2underground.com/groups/management_worklist_service_broker/default.aspx

I was able to use granular SharePoint permissions to make "Sleep" and "ReDirect" not actionable by targeted users.

The options still show up in the Worklist Webpart, but if a user tries to use them, they get a SharePoint "Access Denied" error display in the resulting pop-up.

This isn't a graceful solution by any means, but at least prevented these options from being actionable - which was a firm requirement of the process in question.

In this case, I created a permissions level in SharePoint with only the "Open" permission checked.  (Site Actions / Site Permissions / "Permission Levels" button / "Add a Permission Level" link.  In the "Site Settings / Edit Permission Level" dialogue, under "Site Permissions" heading /  check "Open") Everything else unchecked. (Named this "Limited-2")

I created a group in SharePoint for the targeted users, and set the Site Level permissions for that group to the permissions level created (Limited-2).

This effectively barred access to anything on the site for that group.

I then broke inheritance on the areas of the site the users needed actual permission.  (Go directly to whatever page / list / library they actually need permission. Go to that item's permissions area / "Stop inheriting permissions". Then select the targeted group, and select "Edit User Permissions")

In this case, I set the permissions this way:

"View Only" level for the SitePage that has the worklist.

"Contribute" level for the InfoPath form library (so they can open the forms used in the K2 InfoPath Task / Client Events).

"Contribute" level for the "K2 BlackPearl Data Connections" library (important).

And then any other lists or libraries that the user needed direct access to (I.E. a library webpart that is displayed on the same page as the worklist, gave them "Read" rights, etc). In this case, the K2 Service was enough for other items related to the workflow.