How do i make bubbles on surface of chips?

The bubbles are formed by gases expanding inside the chip as it is heated.

Do this slow enough and the bubbles will escape before the chip hardens (giving it that chip crunch).

Do this fast enough and the bubbles will be trapped.

You could try higher heat for a shorter period of time - or even very high heat to "seal" in the bubbles then finish at a lower temperature.

@SnakeDoc hit the high points of how the bubbles form. I would add that a slight increase in moisture may help create more of a tendency to form bubbles so experiment there, a few drops at a time to keep the consistency you want to work with while getting slightly more moisture for creating the steam expansion.

Here is an article on a somewhat similar technique for inducing potato chips to puff. With them of course you cannot control texture and such, and if they puff you tend to get a single large bubble, not multiple small ones like you seem to be after, but the technique may point you into the direction. Details may require you to experiment. Summary in case page is not accessible: They recommend frying at 320F while gently shaking back and forth until a good portion of the chips start to slightly puff and rise. Then transfer chips to 365F oil. They should promptly puff more fully. Cook until crisp and to desired level. The exact details are probably not what you want, but as a starting point could help with experimenting.