Learn Swedish: Kan du vänta ett ögonblick?

It literally translates to "eye-blink"! It is put together from ögon (eyes) and blick (glance or look). So you are literally asking someone to wait for the blink of an eye.

Why isn't there an att (to) before vänta?

Because kan (can) is a modal verb, which is a helper verb that expresses ability or possibility. Just like in English where you say "can wait" instead of "can to wait", Swedish modal verbs are followed directly by the base form of the main verb without att.

I know the word for "glance" is en blick. Why does this sentence use ett for ögonblick?

That is a great catch! Usually, Swedish compound words take the gender of their final word. However, ögonblick is a historical exception borrowed from German, so it became an ett word. You just have to memorize it as ett ögonblick.

Could I use en stund instead of ett ögonblick here?

Yes, you can absolutely say Kan du vänta en stund?. The difference is just the length of time: ett ögonblick implies a very short wait, like "just a second", while en stund (a while) can mean a slightly longer period.