To get a standing collar, basically you need to use interfacing of an appropriate weight, and sew or iron it between the top fabric and lining/inside. It's pretty simple; cut the interfacing just a bit narrower than you want the finished collar to look (since with fabric on top it'll often add some size), pin it to the right shape as you do the collar- or, as I usually end up doing it, sew the main garment, then pin it on to the right shape and size once the rest is fitted and attach the fabric overtop and just remove pins as I go, essentially making the collar seperately from the main garment (if you're going without a pattern or not great at fitting/drafting, it's much easier that way)- and then sew it up. Basically you're just sewing or ironing an extra, stiff layer into your fabric. Since his cape is a fairly heavy-looking material, if you have a weighty fabric, I'd use a sew-in interfacing, either medium or heavyweight. A good test is to drape the fabric you're using over a piece of interfacing held vertically. If it stays up fairly well, your good. You can also stitch a few layers together if it's REALLY heavy fabric.
(Here's an example for how well the stuff can stand up, from my good old Itachi cosplay; the collar is around six inches tall and with a heavy coat-weight jacquard fabric and lining overtop of it. Ignore the crap attempt at hair and makeup.