Updated Salesforce Interview questions : 

1)How to write 'where' clause in SOQL when have 'group by' clause.

2)how to enforce assignment rules via apex.

3)how to access custom controller-defined ENUM in custom component.

4)in class declaration if we don't write 'with sharing' keyword then it runs is system mode ,so why 'without sharing' keyword introduced in APEX?

5)expaline 'setscale()' in apex?

6)what happend if child have 2 master records and 1 is deleted?

7)how to get all required fields of sobjects dynamically?
8)if user doesn't have any rights on perticular record and have read only acess at object level ,can that user change the record owner?
9)how to avoid salesforce auto focus functinality in visula force page?
10)if we have two objects A and B .and we have trigger on A to insert record in b.But user doesn't have access to B object what happens then?
11)what is the main purpose of extention in SFDC?
12)order of execution in vf page?
13)in which senario 'custom object__share 'is not availble for custom object 'customobject__c'.
14)explain test.setpage();

Ans: 

Test.setPage() method is used to set the context to current page, normally used for testing the visual force controller in test classes.
15)how validation rules excuted ,is it pagelayout dependent or visual force page dependent?
16)how to create instances of sobject at run time or dynamically?
17)what are diff bindings in vf page?
18)what are '__mt' and '__s' in salesforce? 
19)how to reduce internal view state size in salesforce?
18)one master object A is private and other master object B is public then what os OWD for child object c?