This is my favorite subject! Why are words pronounced as they are? Remember I have no authority really for any of this.
There is a limitation in English spelling. We don’t have a way to indicate that two letters are simultaneous. The two letters -n and -e are simultaneous. Think -nnnnn. The -n means to put the tongue on the roof of your mouth and the vowel means to phonate. Long -o since the great vowel shift is now a diphthong, an -uh sound moving to an -ooo sound. If you say all three sounds quickly -uh -oo -nnnn you will feel the -w as your lips move. As you speak in normal conversation the individual letters do not appear and people hear the same sound as the pronunciation of the word “won”.
“Two” is a little harder to see. The double you sound is actually two -u sounds a long -oo and a short -uh one after another. I don’t know which is first. Either way as you move your lips through those two sounds and then to the next vowel you will feel the -w sound in your lips. “Twain” got chopped to “twa” and now the -oo sound from the double -u dominates. Say this rapidly as if you had a dutch NY accent: tuh -oo -ah eggs. As the two elides into the eh of eggs you will hear the -w disappear and the -oo takes over. In scottish they still say twa.
You might want to read a reddit/etymology about this:
There is a lot of guessing and don’t bother if you need authoritative answers but I like it.
https://www.reddit.com/r/etymology/comments/7hjx13/why_do_we_pronounce_the_w_in_twice_but_not_two/
When I was in college (Electronics)...I had a long commute. When I had an early class then a late class, I would finish all homework assignments then hang out in the library. The Oxford English Dictionary was among my favorites.
Still haven’t figgered out “i before e except after c, unless it sounds like ‘a’ as in neighbor and weigh”...weird ain’t it?