when i try to 'check challenge' on the hands on challenge for 'work with GUS at salesforce > GUS at work > Create Work Items', i get the following error and cannot finish the challenge

There was an unhandled exception. Please reference ID: YRPEAQJA. Error: Faraday::ClientError. Message: INVALID_TYPE: SELECT Id FROM agf__ADM_Work__c where RecordTypeId ^ ERROR at Row:1:Column:16 sObject type 'agf__ADM_Work__c' is not supported. If you are attempting to use a custom object, be sure to append the '__c' after the entity name. Please reference your WSDL or the describe call for the appropriate names.

Hello,

I am pretty new to SOQL and I am trying to write a query
List<SObject> quotes = [SELECT Id, Name, QuoteId, Document FROM QuoteDocument];
and I get an error:
"sObject type 'QuoteDocument' is not supported. If you are attempting to use a custom object, be sure to append the '__c' after the entity name. Please reference your WSDL or the describe call for the appropriate names."

I am trying to build a package and I would like to get the list QuoteDocument if it exists in the Organization and also list should be empty if Quotes are disabled for the organization. How can rewrite the statement to achieve this?

Thank you in advance.