What will be crystal field splitting pattern for octahedral complexes if some of the ligands are strong and some are weak field ligands?
Well, the split would depend on: The identity of the metal ion as well as the identity of the ligands themselves. You'd have to consult a spectrochemical series to determine the magnitude of the split caused by the ligands.
Alternatively, you could beam white light through the complex and using the light that appears, determine the wavelength of the light absorbed (the complementary colour) to promote electron(s) from the lower split d orbital to a higher one... This would give you more information as to the magnitude of the split (sometimes, the experimental value will provide an answer that theoretically cannot be determined).