Can this be used to blend colored pencils?

It's my understanding that colored pencils are wax based and this is an oil based blending stick used for oil paint sticks. The oil may emulsify your colored pencils and cause them to blend, but it would leave oil on the paper, and I don't think you're going to want that. You can use Turpinoid to blend colored pencils, and move them like water colors, and it evaporates off the page so it doesn't leave a film.

can these sticks be used for/with encaustic wax?

Yes, they can be used to draw in/on encaustic wax or as a fine layer of color. If you wish to mix them into encaustic medium to make your own color, it is recommended that you allow a small piece of the stick to sit on a paper towel over night and allow some of the additional oils to migrate out of the color. This will prevent your wax from becoming too oily.

Can I mix colors together with this blender

I'm not exactly sure of the question, but the blending stick is basically like the other pigment sticks, but with no pigment. So, yes - you can mix it with other colors of pigment sticks.