How do I attach this horseshoe lucite purse handle (with holes at the bottom)…
… to this lampshade purse which I’ve already knitted?(http://blog.grittyknits.com/ViewPost902.aspx)…
Also, I like how the handles would look on the outside of the purse. What do you think? Or, if I put the handles on the inside, would I do it before/under the lining?
Hmmm. Is that bag even big enough for those handles to fit?! 
Anyway, I’d just whipstitch the handles to the bag using the same yarn. If you put them on the inside, they should go on the inside between the lining and the shell, in my view, anyway.
Thanks.
My purse is big enough for the handles.
So, in essence, the whipstitch is just sewing through the knit shell, then through the hole in the handle, and through the knit shell, like in a circle for the width of the hole?
Yes – you want to try and make the stitches as even as possible, entering and exiting the same place along the top of your bag, and keeping the yarn smooth along the hole in the handle.