Dragonbane leaves secondary skills -- other than magic -- as an option for future rules or campaign settings. It looks like the upcoming Ereb Altor and Trudvang settings are going to take them up on this.
To recap, this is the skills section in the core rules (page 25):
After a good year of our Dragonbane campaign we felt we were missing a few things: Streetwise, Herbalism, and Hard Drinking (a Telrhin staple*).
Herbalism is a big part of Telrhin. We have a long list of medicinal and magical herbs we use for all sorts of things. We even have a very Arduin-inspired section on horrifying diseases: "Unnatural Miseries & Agues". For Dragonbane we decided it was a specialty skill, a subset of Bushcraft. To make that work we're using it as a "stacked" skill: you add it to your Bushcraft roll when searching for or identifying herbs.
Secondary Skills
Stacked skills start at 1, and you can choose to start them as "trained" skills to make it 2.
What adventure is complete without a good pint?
All adventurers start with it. Most people in Telrhin over 10 years old start with it. And sure, you can choose it as a "trained" skill if you want to make that terrible choice.
Herbalism (Stacked)
This is a stacked skill: add it to Bushcraft rolls when identifying plants and magical herbs, and how to prepare/apply them.
Hunters, Mages, and Scholars start with Herbalism at 1.
Streetwise (Stacked)
This is a stacked skill: you add it to other skills rolls like Persuasion, Awareness, Spot Hidden, Myths & Legends, Languages, Bluffing, and Bartering when dealing specifically with the underworld of crime and society's underbelly.
Bards, Mariners, Merchants, and Thieves start with Streetwise at 1.
Learning Secondary Skills
Modified from the core rules on Learning Magic (p.61).
You can learn a secondary skill from someone who already knows it. The lesson takes a week, but you don't get the new skill until the end of the game session. Then use an advancement mark to learn the new skill instead of trying to increase an existing skill level. Make a roll against INT, with a boon. On success you learn the skill.
Advancing in a Secondary Skill
For a non-stacking skills advancing is the same as primary skills (roll a d20, exceed your current skill level).
For stacked skills (like Streetwise and Herbalism), make a check if you roll a dragon/demon, then roll against the stacked skill total. For skills like Streetwise you'll need to remember the stacked skill you rolled against, since they can be combined with multiple primary skills.
* Hard Drinking: our high-school AD&D campaigns had a homebrew skill called "Alcohol Chugging". Don't judge. Some variant has made its way though all of our games set in Telrhin.