Você pode usar o CTE recursivo .
Algo assim
DECLARE @Table TABLE(
Supervisorid INT,
Empid INT
)
INSERT INTO @Table SELECT 3, 4
INSERT INTO @Table SELECT 3, 5
INSERT INTO @Table SELECT 3, 8
INSERT INTO @Table SELECT 4, 9
INSERT INTO @Table SELECT 4, 10
INSERT INTO @Table SELECT 4, 11
INSERT INTO @Table SELECT 8, 12
INSERT INTO @Table SELECT 8, 13
DECLARE @ID INT
SELECT @ID = 3
;WITH Vals AS (
SELECT *
FROM @Table
WHERE SuperVisorID = @ID
UNION ALL
SELECT v.SuperVisorID,
t.Empid
FROM Vals v INNER JOIN
@Table t ON v.Empid = t.Supervisorid
)
SELECT SuperVisorID,
COUNT(Empid) Total
FROM Vals
GROUP BY SuperVisorID