I have an opportunity (child) with a lookup borrower__c to account (parent). How can I query the account record,given opportunity record I'd without using borrower__r or borrower__c ?
@CommonCoreTawan is correct. I don't understand why you need to do this without using the "borrower__c" or "borrower__r field".
Considering you want to only use the opportunity Id and NOT Borrower__r. You could use a nested query such as the following which uses the Opp Id as you requested.
Id oppId = '0061I00000gdjafRQR'; List<Account> liAccount = [SELECT Id, .... FROM Account WHERE Id IN (SELECT Borrower__c FROM Opportunity WHERE Id =:oppId)];