Hi Naveenraj,
As you know N partners can be assigned to a opportunity, so first of all you need to know which BP you want to show (partner function) and be sure that is a 1:1 relationship between the Opportunity and the BP.
Then you can create the context node using the following path:
BTADMINH/BTHeaderPartnerSet/choose which reationship suits for what do you want to retrive, if the relationship will be 1:N then you will have to create a value node and map it manually from the result of the relationship.
Regards,
Luis