A wish list is just another database table. When a user adds an item to a wishlist, a record is added to a databse table that contains the product ID and the Item ID
First you would need to use Security Assist to log the user in.
the authenticate user behavior on the login page will set a session variable that contain s the logged in users ID.
on the product page, you would add the Add to wishlist button, and a DataAssist insert record behavior. the insert record behavior would add the user id and item id to a wishlist table.
You can then create a view wishlist page that shows the items in the wishlist with an add to cart button so that wishlist items can be added to the cart for purchase.