Thank you for stopping by the community and posting a question. Lacerte is not able to add a Notes column to the Client List. What you would be able to use in Lacerte is a Custom Filter, Client Notes, or Sticky Notes. Please see these knowledge bases about them:

Creating a Custom Client Filter

https://proconnect.intuit.com/community/help-articles/help/creating-a-custom-client-filter/00/4032

Creating Client Notes

https://proconnect.intuit.com/community/help-articles/help/creating-client-notes/00/4277

Sticky Notes - Intuit Academy

https://www.youtube.com/watch?v=DJhPRfdcopU

Using Sticky Notes

https://accountants-community.intuit.com/articles/1858521-using-sticky-notes