According to the electromagnetic spectrum, gamma rays have the shortest wavelength. therefore, gamma rays have frequency.

Gamma rays have highest frequency.

Gamma rays are a type of electromagnetic radiations and these rays are also used for the purpose to treat cancer. When we look at the electromagnetic spectrum, these rays fall above the x-rays. Gamma rays are produces by atomic nuclei.

I believe the answer is: Highest Frequency

frequency refers to  the number of cycles that happened during one unit of time by a body in periodic motion.
Frequenct is calculated with this formula:

f = c / λ

c = wave speed
 λ = wave length

So, as the wavelength got smaller, the frequency would got higher.