Shift registers. What, how and why?
You can chain as many shift registers as you want.

Most commonly, these displays are multiplexed. Only one digit is lit at a time, cycling though all the digits fast enough, so the eye can't tell. This is however not very good practice for 28 digits, as the brightness will become 1/28th (though you could create groups of digits, and multiplex those groups separately).

There are specialized chips that do this multiplexing for you. E.g. the Max7219. This chip can multiplex 8 digits, with 8 segments. So you'd need 4 of these to light up 28 digits.