VO Extension is tool (JDeveloper) dependent but can be done manually by using below steps.
Steps to extend VO: 
Create new VO  xxxxx_StandardVO.xml by renaming the standard VO StandardVO.xml (from server).
Edit below sections of VO according your customization need.  
<ViewObject>
Name = New VO Name  
Extends = original VO Name with complete path
ComponentClass = NewVO associate file with complete path
<SQLQuery>
Update the SQL with new changes.
<ViewAttribute> -  Not required If change is in where condition or existing SQL logic
If adding a new sql field,we need to add ViewAttributes for new field.
Example - 
<ViewObject
   Name="  xxxxx_StandardVO "
   Extends="oracle.apps.application.subapplication.common.server.  StandardVO"
   BindingStyle="OracleName"
   CustomQuery="true"
   ComponentClass="xxxxx.oracle.apps.application.subapplication.common.server.xxxxx_StandardVOImpl"
   UseGlueCode="false">
<ViewAttribute
      Name="NEWFIELD"
      IsUpdateable="false"
      IsPersistent="false"
      Precision="30"
      Type="java.lang.String"
      ColumnType="VARCHAR2"
      AliasName=" NEWFIELD "
      Expression=" NEWFIELD "
      SQLType="VARCHAR" >
      <DesignTime>
         <Attr Name="_OverrideAttr" Value="true" />
         <Attr Name="_DisplaySize" Value="30" />
      </DesignTime>
   </ViewAttribute>
Create associated java file xxxxx_StandardVOImpl.java
package xxxxx.oracle.apps.application.subapplication.common.server;
import  oracle.apps.application.subapplication.common.server.  StandardVOImpl;
public class xxxxx_StandardVOImpl   extends StandardVOImpl {
    public xxxxx_StandardVOImpl()   {
    }  }
Compile and generate class file (xxxxx_StandardVOImpl.class
Create a OAProject.jpx file 
<?xml version='1.0' encoding='windows-1252' ?>
<!DOCTYPE JboProject SYSTEM "jbo_03_01.dtd">
<JboProject
   Name="OAProject"
   SeparateXMLFiles="true"
   PackageName="" >
   <DesignTime>
      <Attr Name="_ejbPackage" Value="false" />
      <Attr Name="_NamedConnection" Value="DBConnection1" />
      <Attr Name="_version" Value="10.1.3.41.57" />
      <Attr Name="_jprName" Value="OAProject.jpr" />
   </DesignTime>
   <Containee
      Name="server"
      FullName="oracle.apps.application.subapplication.common.server"
      ObjectType="JboPackage" >
   </Containee>
   <Containee
      Name="server"
      FullName="xxxxx.oracle.apps.application.subapplication.common.server"
      ObjectType="JboPackage" >
   </Containee>
   <Substitutes>
      <Substitute OldName ="oracle.apps.application.subapplication.common.server.StandardVO" NewName ="xxxxx.oracle.apps.application.subapplication.common.server.xxxxx_StandardVO"   />
   </Substitutes>
</JboProject>
Create server.xml file 
<?xml version='1.0' encoding='windows-1252' ?>
<!DOCTYPE JboPackage SYSTEM "jbo_03_01.dtd">
<JboPackage
   Name="server"
   SeparateXMLFiles="true"
   PackageName="xxxxx.oracle.apps.application.subapplication.common.server" >
   <DesignTime>
      <Attr Name="_ejbPackage" Value="false" />
      <Attr Name="_version" Value="10.1.3.41.57" />
   </DesignTime>
   <Containee
      Name="xxxxx_StandardVO"
      FullName="xxxxx.oracle.apps.application.subapplication.common.server.xxxxx_StandardVO"
      ObjectType="ViewObject" >
   </Containee>
</JboPackage>
Place all files at respective locations and run 
  JPX Importer