Do German universities require a YKS ranking from Turkish applicants?

There is no ranking threshold set by German universities, but YKS still matters for Turkish school leavers, because it decides whether your Lise Diploması gives direct university access.

How Turkish school-leaving qualifications are assessed (anabin, the KMK database used by universities and uni-assist, and the information sheet of the German missions in Turkey):

• Lise Diploması alone (12-year general secondary school): no direct access; you first attend a Studienkolleg and pass the Feststellungsprüfung.
• Lise Diploması + YKS with placement (proof of the YKS result and of placement in a degree programme at a Turkish university): direct, subject-restricted access to German universities for subjects related to the programme you were placed in. The ÖSYM result document and the placement document are required.
• Completed Önlisans (2-year associate degree) or successfully completed years of study at a Turkish university: direct access to related subjects, depending on the case.

What universities do look at once you have access: your converted grade (Lise grade and, for some universities, the YKS result), the subject's NC (numerus clausus), the required German or English level and any subject-specific tests. A few programmes with local admission procedures set a minimum converted grade; that is the closest thing to a "ranking" requirement.

Check your own case in anabin ("Schulabschlüsse" → Türkei) and on the uni-assist country page for Turkey, and confirm with the university's admissions office if your programme is not clearly related to your YKS placement. The rules can be updated by the KMK, so verify them for the semester you apply for.