You have at least one problem, maybe two.
1. You are not understanding the problem presented in the challenge Your responses are not satisfying the challenge. For example there is no response “a and b are equal” in the solution for the challenge. In the case of num is 0 you should simply return “zero”
checkSign(10); // should return "positive"
checkSign(12); // should return "negative"
checkSign(0); // should return "zero"
The example problem and the solution are not exactly the same so copying the example into your solution without modification will not work.
In the example problem they are comparing two arguments a
and b
.
There are three possible responses based on the condition of a
and b

 “a and b are equal” tested with conditional
a===b
,
 “a is greater” tested with conditional
a > b
 or “b is greater” the only other possible condition
In the challenge you are comparing one argument named num
against zero.
There are three possible responses in your return statement. You will need to create conditional tests to determine which of these apply to the num passed to your function.
 “zero”  you will need to create a test conditional here
 “positive”  and another test conditional here too
 “negative”
2. You may or may not understand the ternary operator
Other than pasting the example solution you haven’t shown that you understand using ternary with multiple conditions. If you are unsure how that works maybe you should test your logic using if else structure first and once you are returning the correct response modify your code to use multiple ternary operators.