What is the ideal and realistic way to create freckles for a shoot?    I was thinking about using pencil eye liner or brow liner ???

A lot of people use brow pencils in particular because their texture is a little dryer and stiffer than a regular eyeliner and they give a more subtle pay off of color. You could definitely use both if you wanted! As a naturally freckled person myself, I can say that freckles have many variations in sizes and even depth of color and that's the key to making them look realistic. I have seen makeup artists actually use two pencils at a time, held or taped together, to lay an over all base of freckles on a wide area before adding in the individual detailed ones. The more random  and less evenly spaced the placement is, the more natural they look.

Thanks, this is helpful !!!  In the past, I just added more in photoshop ......