So last night a Random Encounter guy with a red lantern ran up to me an GAVE me Speed Up Without Trace FOR FREE. What follows is a concise account of the actions which I BELIEVE triggered the event. Be warned, your milage may vary.
1. Every day I was giving Feng Si, located on Peachblossom Island in Suzhou, Ling Wine (can be bought from a Farmer Shifu). I would do this 20 times (20 gifts is the daily max), giving her the stack 1 item at a time. Incidentally Ling Wine is also an excellent wine to use to level your tolerance.
2. Every day I would visit all three trees where the Bird Eggs spawn. I will not disclose their locations, but if you're giving Feng Si the Ling Wine then you're very close to two of them.
3. Every day I would perform You Chengren's daily quest. He is located in Windblown Valley just south of Suzhou, at a crossroads. His quest is to target him and use this medicine that he spawns in your inventory, then listen to him rant.
The Random Encounter guy ran up to me while I was afk at the Taoist Temple south of You Chengren. You can actually see it from where he stands. Around back is a tree; I was standing under said tree when the encounter happened. I don't know if this is actually what triggered the event, but I know the system is far deeper than many of us get credit for.
The bad news is that the book you get from this is bound. There's a way to get an infinite number of UNBOUND Speed Up Without Trace books, but that's my secret. Lol, besides, a quick google search will show you the translated write up most of us used to figure this thing out.