ParentGetter.cls

static void someMethod() {
    List<SObject> sobjs = [
        SELECT
            Id,
            Name,
            AccountId,
            Account.Name,
            SomeCustom__r.Id,
            SomeCustom__r.Name
        FROM
            Opportunity
    ];

    Schema.DescribeFieldResult fieldResult = null;
    Schema.SObjectField field = null;
    
    /* print Opprutunity.Id and Opportunity.Name */
    System.debug(sojbs);
    
    /* print Account.Id and Account.Name */       
    fieldResult = Schema.Opportunity.Account.getDescribe();
    field = fieldResult.getSObjectField();
    System.debug(sobjs.getSObject(field));
    // or
    System.debug(sobjs.getSObject('Account'));
    
    /* print SomeCustom__c.Id and SomeCustom__c.Name */
    fieldResult = Schema.Opportunity.SomeCustom__c.getDescribe();
    field = fieldResult.getSObjectField();
    System.debug(sobjs.getSObject(field));
    // or
    System.debug(sobjs.getSObject('SomeCustom__r'));
}