What kind of abs can I expect for doing 30 jackknives a day?

Unfortunately, probably none. Crushing tons of reps doesn’t equate to more visible abs, they just get stronger. Doing abdominal exercises and getting abs is a common misconception. The truth is, your abs begin to show through 3 Main Factors.
1.Diet
2.Cardio
3. Ab Exercises
I learned this through my own experience of eating crappy food, not running much and crushing hundreds of abs per day without ANY results.
Your diet should be your main focus in achieving abs. You can read about it on http://bodybuilding.com , they have some great articles. The next step should be creating a consistent habit of cardio 3-4 times per week. I would say that intense short burst cardio is the way to go, however, steady state 30 minute is fine if your just getting into it. Lastly you should focus on ab exercises. There are more and less effective ones you can do. Some that have worked for me are weighted exercises with twists and turns, again search in the link above, they have great examples.
Don’t get discouraged if you don’t see results after a week, I can’t tell you enough how many times that happens and people stay in a constant state of “losing weight” because they can’t execute a plan to the end.

Good Luck! 🙂

Wanbasion Black Stainless Steel Knife Set, Sharp Kitchen Knife