You haven't said it specifically, so I will assume that you are no longer in school. You could still be in school but, of course, not yet have the diploma. My answer will be directed toward someone old enough to have completed high school but who did not graduate or at least who has dropped out.
There is no definite answer, as the hiring depends not so much on the job as on the employer's preferences.
There are many kinds of jobs one can get without that diploma--if someone will hire you. You can learn many jobs as you do them, and often that works better for the company, as you will then know the job their way from the beginning, but the diploma makes a statement that you stayed with it, that you didn't quit, that you cared enough to accomplish that goal.
It is not simply skills that you learned en route to your diploma. It is the fact that you earned it. You do have an option. There is the GED, or General Educational Development. Some people call it the General Equivalency Diploma, which is technically correct but which is a fair definition.
A good friend of mine was just not cut out for high school and went in some unfortunate directions. However, he did pursue his GED, acquired it, and went on to fine career in the U. S. Navy.
Many employers respect the GED at least as much as the regular High School Diploma because it proves that you did take that step to get back on track. The GED can open many doors for you. Here is a link to good info on the GED. It is from Oregon, but the process is pretty much universal.
Now, as to some jobs you might be able to get without the diploma or GED:
Some areas still have newspaper delivery, and a sizable route (motor routes especially) can provide some good money. Some routes are door to door home delivery, and some are bulk drops and service to retail outlets.
Other delivery jobs might work out, too. Cleaning companies are fairly liberal sometimes as long as you can show them that you will do a good job and be a reliable, faithful employee.
Painting houses is a possibility, as are carpentry and some other construction work.
You might be able to start your own business, even quite small at first. You would not need any kind of diploma, but you will need knowledge and the necessary skills for that particular business. Also, if you need financing, that diploma once again plays a role.
Farm work, yard work, pet sitting or walking, window washing, and car detailing/cleaning are possibilities. If you are good at it, you might be able to offer services as a computer consultant to a lot of people who use them but are not really knowledgeable about them.
Some factories and warehouse will still consider people who do not have diplomas, but that is becoming rarer and rarer.
We, of course, don't know what skills you already have or what things interest you, but some other things to think about might be: photography (assisting in studios or at weddings, etc.); bakery work; grocery store work (stocking, bagging, and other work, all of which can sometimes lead to good positions in the store for those who earn them); driving a cab (if you are of age and have a good driving record and can obtain the correct license); working at a movie house (ticket selling, concessions, etc.); or doing repairs (this could include small appliances, cars, or even sewing.
Well, let's send this on its way and find out what other people suggest. Stay with it, and good luck. Whatever you do find, though, give it your very best, and you will see good things happen.