Ricercate, passaggi et cadentie
Ricercate passaggi et cadentie, per potersi essercitar nel diminuir terminatamento con ogni sorte d'istrumento: et anco diversi passaggi per la semplice voce.
It contains possible ornaments. Like many of its contemporary sources it uses an example of two notes (an interval) and then shows how you could use an ornament to go from one note to the next. In a type of table-format the book suggests several options for the same interval; by learning those by heart you get a sense for the style and possibilities.
Interesting about this treatise is the ricercares. Although the text does not explain how to improvise one, it does suggest that you can practice ornaments by improvising new ricercares.
A modern edition by Richard Erig exists. It can be found on IMSLP, but I'm not certain how legal it is: