get List of Item from CDT

Do you want only the attributes of the CDT Type? If you want the attribute fields as well as the values, I would suggest another approach - use the a!toJson function.
Eg: If local!cdt is a CDT with data like this: {id: 1, customerId:23, contacts: {"contact1", "contact2"}} etc, you can just use a!toJson(local!cdt).

If you just want the attributes of a CDT - there is another solution:
Assume that the type of your CDT is Customer. Then you can find the attributes in the Customer CDT as follows:
fn!split(fn!stripwith(fn!tostring(type!Customer()) , "=[] "),",")

It will return all the fields in the CDT as an array

Yes you will have to create a a!queryEntity() if you want only specific columns in your result and you can make it paraterized.
please refer below link for detailed comparision between Query Rules, a!queryEntity()          and queryrecord().
forum.appian.com/.../Querying_Data_From_an_RDBMS.html

@vijayy700, the user who posted the question wants only the information about the fields in the CDT, not the actual data from DB(or the data related to those fields in the DB). The attached screenshot by the user clarifies that.

So, queryEntity()/queryRecord() is not needed since it does not solve the problem that the user has

@joanneh, for your CDT in the screenshot, the expression will change to:
fn!split(fn!stripwith(fn!tostring(type!OPS_JobOrder()) , "=[] "),",")

Probably another solution which does not rely on splitting is:
apply(xpathsnippet(_, "name(*)"), xpathsnippet(toxml(type!YOU_DATA_TYPE()), "/*/*"))

@stefanh791 Never thought to use xpathsnippet()/toxml() to accomplish that. Very slick!

Yes, I also never thought about xpathsnippet() and toxml() to accomplish this. Cool!

You are welcome :-)

Your ideas are brilliant! I use @chetany's way at first but never realise @stefanh791's way works too!

By the way, may I have a follow up question on @stefanh791's solution?
In the line <type!YOU_DATA_TYPE())>, the scipt in my application looks like the following:

'type!{abc.def-ghij.com}MY_DATA_TYPE'()

Is there any way that I could making the item MY_DATA_TYPE variable like? so I could replace it with different input?

I have thought of using something like:

concat("'type!{http://abc.def-ghij.com}" & ri!dataType & "'()")

But it doesn't work....

@joanneh If you are trying to pass in a string "cdtName" it probably won't work. If you are passing in type!myCDT into ri!dataType you could do toxml(cast(typeof(ri!dataType), {}))