Hello, I got a question for retriving data. For example, if I use code like this: <apex:outputtext value="{!Case.Owner.Name}" /> and I can get a text show on my web page. But how can I know where does each value after dot come from, is that simply (object name) . (field name) . (data wanna retrive). But how can I know the exact name of data that I wanna retrive?  The example I showed is a bad example, cuz I assume that the name of data I wanna retrive maybe call Name, yet I dont know where to find it.     Thanks for helping.

I submitted my work and I received this error message. The challenge says nothing about adding a field with this name. 

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: REQUIRED_FIELD_MISSING, Required fields are missing: [Discount_Percent__c]: [Discount_Percent__c]