A good course to enhance your CV totally depends on your background and the job you are applying for. You can visit Coursera and Udemy sites and choose the domain you are willing to apply to and then search for relevant courses. Most of the courses have on these platforms have ratings and will tell you whether people have liked it or not. This will help you decide whether you should be pursuing it or not.
That totally depends on you educational background- the courses you’ve undertaken, the industry you’re looking forward to enter or are currently working in. Google has a bunch of free online courses which you can check out.