score:3
From the ever-helpful Turkish Airlines website:
At that same page, it states that for Economy class passengers, you are only allowed one piece, which can be maximum 8 KG; for business class 2 pieces (each 8KG).
This does not include the personal item, as illustrated above. Normally, personal items (purses, laptop bags, etc.) are not weighed. So, theoretically you could have a laptop bag that weighs more than 8 KG, as long as it fits under the seat.