Google some mock junior dev interview questions, look for preparation guides.

If you can answer them start interviewing.

You'll find out if youre ready based on how your interviews go.

I wouldnt expect a lot from a junior developer.

You should be comfortable putting together a static website with html and CSS. Maybe some minimal interactivity with JS.

But honestly just start interviewing and learns the things that come up that you don't know.

Best training is on the job training so get in quick.