Can I connect an SD card shield to Digispark ATtiny85 board?
In short I am going to say NO.

The flash is too small to adequately run the SD library as well as the rest of your Arduino code.

The RAM is also underpowered for what is needed to properly access files on an SD card.

Having said this, I am sure there are some clever software engineers that could write a cut down SD card library to do limited commands. Overall this is too hard for the beginner - Just buy an Arduino Uno/Mega/Due and avoid the unnecessary hassle.