How can I display text on OLED?
Just guessing but looks to me like you read the CAN message and print it character by character to the Serial console but you don't save those characters in a buffer as you get them from CAN.read().
So when you then try to display.print((char)CAN.read()); at that point there are no more characters to available for the CAN.read() to read so nothing is printed by the display.print().
So what you need to do is to read the characters into a buffer so that you save them after reading them so that you can use the text string for other purposes.