A given provider is not obliged to fill in the ItemList attribute. In fact the ItemList attribute is a rather new feature and I suspect most existing providers are written before this feature was added, i.e. the attribute will most often be absent/empty.

Some providers simply provide too many data items or the data items provided are very variable. There are even providers that can publish an infinite number of data items. All in all for many providers this attribute doesn't make sense and for that reason it is not mandatory.

In your case I can tell from the name, IDN_RDF, your provider is providing data from an RDF (Reuters Data Feed). This means data from the Thomson Reuters IDN network. There are simply millions of data items on this network and it wouldn't be practical (or desirable) to have them in a SymbolList.

so I don't know how to send item request .

Not sure I understand. You do not need a SymbolList to fire an item request. You'll of course need knowledge of some data item name and you cannot get that from the feed itself. Sorry.

In your case, IDN, the data item names are called RICs (Reuters Instrument Codes). Thomson Reuters used to have a so called Data Guide which was a PDF guide to how RICs are constructed. It used to be hosted on this page. I cannot find it anymore as the page has become meaningless. You'll need to ask TR for it.

To get you going try sending item request for data item name TIME from service IDN_RDF. The contents of that one is pretty meaningless but any user (afaik) has access to it and it will guarantee you an update at least once per minute. So perhaps good place to start? Alternatively I can recommend developing first against an emulator and when your application works you can move it to point to a real-life feed.

Hope this will get you going.