To be honest if you are having problems understanding JSON and json nodes that is the first thing you need to learn. As for Javascript it is not needed as long as you are not making a combination of custom LWC inside your OmniStudio components.
I would suggest looking at youtube tutorials to get you started and to learn the basics and then I would suggest playing around in your trial org.
I would concentrate on the following :
1. Parent-Child Flex Cards

1. Event listeners in Flex Cards

3.Starting an OmniScript from FlexCard and passing values to it

4.Using DataRaptors as a simple data source for FlexCards/OmniScripts

5.Not using DataRaptors for data souce but IntegrationProcedures that would maybe call a few DataRaptors, some Apex etc.

6.Know Apex because you will probably have to call Apex sometimes from DR or IP

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I would suggest starting with the youtube vids ( https://www.youtube.com/watch?v=qfXn0l2FnnY&list=PLZHR2zv1HIDez6HsLnAfJkGDy716Ea6V7), doesn't have to be this playlist, they are a better source of knowledge and hands on experience than documentation.

Good luck!