What type of permission allows for comments but can't delete or edit cards or lists?

[Seven]

I need to know how to give clients the ability to comment on cards and lists but not delete comments, attachments, cards or lists. 

Is this possible?

[Alex W]

That would be the Observers feature, available only to Premium and Enterprise workspaces. You can read more about it here: https://help.trello.com/article/732-adding-observers-to-boards

I can see you have one Premium workspace so you should be able to use this feature there.