One classic example where photons exhibit wave-like behavior is in the phenomenon of interference. Interference occurs when two or more waves overlap, either constructively (adding up to produce a larger wave) or destructively (canceling each other out).
In the case of light, if we consider a double-slit experiment, where a beam of light passes through two narrow slits and creates an interference pattern on a screen behind it, we can observe the wave-like nature of photons. When individual photons are sent through the double slits one at a time, over time, they accumulate on the screen and create an interference pattern that resembles the pattern produced by waves.
This suggests that each individual photon passes through both slits simultaneously, interfering with itself, and producing an interference pattern characteristic of wave behavior. The probability distribution of photon impacts on the screen builds up to form regions of higher and lower intensity, analogous to the bright and dark bands of an interference pattern produced by waves.
This experiment demonstrates that photons can exhibit wave-like properties, such as interference, even though they are elementary particles with no mass. It is one of the fundamental pieces of evidence supporting the wave-particle duality of light and other quantum particles.