Mali Uromastyx: Stick thing sticking out of Femoral Pore

Waxy Secretions

From the photos you have provided it looks like a waxy secretion from one of the femoral pores, this is normal.

These secretions are used to attract mates and mark territory, both sexes of some uromastyx species will have pores where as others only the males will. They can cause discomfort if they become too large, giving a warm bath can loosen these secretions if they do not come off on their own.

Sexing Mali Uromastyx

This can be done similar to bearded dragons or geckos, you will see hemipenal bulges when lifting the tail. I have never tried shining a light through a uromastyx's tail to see however you can give it a shot (like this bearded dragon).

Note In the photo above you can also see the waxy secretions coming out of the pores.

From Reptile Magazine:

Determining sex is tricky at first. Both sexes possess femoral pores, and when reared in captivity, coloration is no longer a reliable indicator of sex.

Looking for hemipenal bulges under the tail is the safest sexing method. Gently arch the tail over the lizard’s back. Study the underside of the tail just behind the vent opening. With females you’ll see the base of two ligaments, one on each side of the vent, angling down toward the tail tip. Just their base is visible, so it will look like a small upside-down V sitting just above each corner of the vent. With males the hemipenes sit on top of these ligaments, largely masking them. In this case, the pattern looks more like two parallel lines sitting just above the vent pointing toward the tail tip.