Hello Lohit,
So you have defined the field in the table and linked the search help as well (through se11)?
Then you have ensured that the relevant object (Initiative = IPO) is associated with the advanced search service through SPRO - > Portfolio Management -> Global Customising -> Process & Service Settings ->Define Services. In here you link/add the object type to the service for Advanced Search
Now under Global Settings -> Define Custom Field configuration under the field configuration area you add in the field and link it to the service for advanced search. You also specify under UI Configuration that the field is enabled, etc
Under config node 'Assign fields to views/subviews' you create a group ID and assign the field to a field position
Under config node Portfolio Dependant Settings -> Define Portfolio Types then Portfolio Items Override you can specify this field to be required by a specific Initiative/Item Type. Unfortunately this is the only option you can choose here - i.e. you cannot through standard enable the field only for specific types - you can simply make it required for a specific type. You will need to make an enhancement in order to do this but perhaps this will meet your requirement?
Hope this helps
Regards,
C