The Client Checklist is not part of ProSeries Basic.

As George says, you do have the option to transfer your clients to Professional and print out the Checklists (you will still prepare the actual tax returns with Basic).  However, from what I remember, I was not impressed with the Checklist.  You may consider creating your own generic Checklist to give to each client.

In the event you want the clients to have a very detailed list with their specific items (more detailed than the Checklist), you can give them the "Organizer".  Again, that can only be done within Professional, but you can transfer your clients there to do that.  However, the "Organizer" does cost money (either as a Pay-Per-Return or a $298 'package' with unlimited Organizers).