Portland cement & sand. Easiest if you just buy bags of pre-mixed stucco/mortar.
If you just want a thin coat (stucco usually winds up around 5/8 thick) you might consider thinset mortar. I wanted to plaster over a block garden wall a few years ago and used it because I find it much easier to apply than regular stucco mortar.
I don't know, but I am sure that if you do Google and YouTube searches for something like "stucco brick wall" you will see lots of good information on what the use, how to apply it, etc.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.