You can get to know the tools for API automation very easily. The main things we should know is the language we are using for the project. The languages such as Java, Python, Groovy which are the basic language every testers must know. Deep knowledge is not required at all. Basic will also do. And gradually, you keeps on learning the languages, the more you explore, more you become knowledgable.
So, For any API automation, Either you can choose Smartbear product or else you have open-source product also such as Rest-Assured, Unirest, etc. But with Smartbear product you get support also if you face any problem. I have been using ReadyAPI from last 2.5 years. So, I'd suggest to go for Ready API.
The market is really growing and every year new tools are coming on the way. So, you must have great understanding on market value also for the tool. If you see, outside you will get to know, How Ready API/Soap UI knowledge is required for any interviews. At least for manual purpose many companies uses SOAP UI only.
Testing courses are really required to sharpen you skills and to work for corporate world. Smartbear has its own API automation courses available on its website. Some of them are free like documentation on Ready API/SOAP UI. And some of them are priced. But its really worth to get through that testing courses to make yourself more valued according to market standards. Else, you can take help from API experts also. They can guide you properly if you are really new to API testing.
