XML questions don't always get much love around here. Here's what you are looking for:

EXEC SP_xml_preparedocument @Payrollhandle OUTPUT,@Payrolldoc;

SELECT A.*, B.AsstDaysOfficeID

FROM

OPENXML(@Payrollhandle,'Payroll/Doctor/WorkDays/Office',8)

WITH

(DoctorID INT '../../@ID',

WorkDaysOfficeID VARCHAR(10) './@ID') AS A

OUTER APPLY

OPENXML(@Payrollhandle,'Payroll/Doctor/AssDays/Office',8)

WITH

(DoctorID INT '../../@ID',

AsstDaysOfficeID VARCHAR(10) '@ID') AS B

WHERE A.DoctorID=B.DoctorID AND A.WorkDaysOfficeID=B.AsstDaysOfficeID