Bear in mind that the trigger will fire once for all rows affected in a batch. If you ever insert more than one row into your table in a single batch, your trigger will not work as expected.
Update your trigger to account for multiple rows:
ALTER TRIGGER trg_Student_Insert
ON test
FOR insert
As
BEGIN
SET NOCOUNT ON;
INSERT INTO TrgTest
SELECT
'Waa qaatay Alaabtii = '
+ CAST(Taken as nvarchar(30))
+ ' Taarikhdu mar kay ahayd '
+ CAST(GETDATE() as nvarchar(30))
FROM
inserted
WHERE
Taken = 'Yes'
;
INSERT INTO Muqadan
SELECT
'Muuqaadan Alaabtii = '
+ CAST(Taken as nvarchar(30))
+ ' is Registred date markuu ahaa '
+ CAST(GETDATE() as nvarchar(30))
FROM
inserted
WHERE
Taken = 'No'
;
END