better description and more test cases are required

The description has many typos, and does not provide adequate explanation. Anyone who knows what JSON is will likely find this kata far too simple; given the difficulty level, it would be appropriate to explain JSON in the description, or at the very least, provide a link to an explanation. The single example is not enough.

Not set up to have variable accesssed by function

The word 'easier' is misspelled.

Instructions are unclear.

Typos and capitalization errors in the description. Also Kata only really makes sense when you look at the test cases, so description should be more detailed.

The description should elaborate on what is required. Without test cases this would have been much more confusing.

The description suggests that one should create a JSON compatible object, but the tests only compare strings.

The initial solution doesn't reflect that you want to use a.toJson, e.g. change the Object prototype.

For basic tests you should use strings to compare, do not show the JSON.stringify function.
If you would want to make this much harder, you can actually delete the JSON object while saving JSON.stringify in a hidden place, remember to delete require and module.require to prevent recovery of the JSON object using the require("vm") module.
You should also test that circular objects need to throw an error.

This kata's description makes no sense.

JSON is a string format: if you want the result to be JSON, it should be the same as calling JSON.stringify.

There are no example tests, and the examples in the description make it look like you want a method that returns the original object.