Your doctor will be affiliated with a hosptial system that often offers their own. I would ask the oncologist about this first before doing the ONS one. Most of the docs in our area do it this way. they also give you more info than just administration of chemo that will help you on the job. Cheaper also.
It really just depends. Some organizations have their own programs, others use the ONS one because of its comprehensive nature (it isn't just chemo admin, but I digress). Definitely check with your employer before you spend your own money, though!
If you look at Oncology Nursing Society, they can tell you when a chemo provider course will be available in your area. The first time you take the course it is not just about chemo administration. I would recommend taking it, particularly if you are new to oncology, because the learning curve is pretty steep to go to outpatient oncology with no experience.
They should provide training to you in chemo administration according to their policies and procedures. The ONS certification may be what they use, but if it's required, most facilities will pay your registration costs and sign you up with fellow new hires. Our floor only does the official ONS chemo classes every six months for those new to oncology. They give the new hires basic chemo training prior to the course.
Please note there is no process that results in chemotherapy “certification” on a national level. ONS does not have or endorse any program that results in chemotherapy “certification”. The ONS Chemotherapy/Biotherapy Certificate Course is a new online offering and is no longer offered as a live program. Successful completion provides you with CNE credit and a Provider Card from ONS, and a Certificate of Added Qualification from ONCC. More information is here: https://www.ons.org/chemo-provider-course.