ST ST25R95 - NFC chip - Impedance of transmission lines
My doubt is about the black lines shown on picture above, the
  transmission lines. Should they have 50 ohms? or 27 ohms? I think it
  should have standard 50 ohms but I would like to have sure about that.


The device operates at 13.56 MHz and the wavelength of 13.56 MHz is 22 metres in free space and about 15 metres on a typical PCB. So, the golden rule is that if your tracks are longer than about one-tenth the wavelength then you should start to consider using transmission line calculations.

Are the tracks likely to be close to anything like 1.5 metres long is the question you should consider. If not then don't worry about matching because it won't make a difference practically.

 I've used 13.56 MHz because the signals are largely sinewave at 13.56 MHz. If it were a clock of 13.56 MHz then I'd be considering t-line math if the track length was more than 20 cm.