Zonk actually isn?t very good despite what a lot of people say. It only comes into play in very specific situations and in very specific match-ups and overuse will leave you often getting killed. Reasons why this is, is because if you charge ex zonk, you either can?t tech, or can?t AA with back strong. If you?re using regular zonk constantly, you will have difficulty doing max dmg punishes because you can?t use your fierce. Also, just having to keep in mind when you have zonk held down often leaves you a bit flustered or you?ll end up getting random zonks when you don?t want them cause you forgot you?re charging. To deal with held zonks, throw a normal, jump or dash then release.
Whenever I?m using zonk to blow past fireballs, which is about the only time you should use it unless you know it?ll hit, use the fierce button for zonks. I charge it with my right ring finger and to release, usually throw a rock or dash. If you?re trying to combo into bingo, you have to either know when you?re only charging level 1 (or was it 2?) zonk and comboing with either strong and fierce cause jab doesn?t have enough hit stun for a true combo. If you get to a level 3 zonk, strong no longer combos into zonk either. So that means, to reliably combo into regular zonk, u have to zonk with jab and have the combo or setup in mind before you start it.
For example, if you really wanted to combo into zonk, you could jump-in, hold jab, press s.mp (hit confirming by now), c.hp xx zonk. This is the only real good way to combo without taking risk. The other methods you can use are use level 1 zonk and do things like, f+mp, c.mp xx zonk. I see sabr3 use a lot of zonk combos and its cause he?s committed to memory how long it takes to not overcharge it. This is pretty hard and requires lots of experience. If you?re just starting out, I recommend you don?t use zonk for much other than guaranteed max range situations, reversals against poorly thrown specials (against dash punch for example) or in fireball wars.
Once you get comfortable with all of cody?s combos, I recommend adding rh rk, fadc, zonk for hefty dmg. Cody gets probably 400+ dmg off this jump-in combo alone if you tack on j.rh, c.hp xx to the above.