SPI I2c and CAN protocol frequently asked questions

On saturday i have got a interview for SPI, I2c and CAN protocols . I have got working knowledge with all these three . Eventhough for CAN we have used node to node . It is a development board . Value typed in hyperterminal will passed to controllert hrough UART and transferred to another board through CAN . I wish to know about the frequently asked question in these three topics . I have recently been asked how the slave device knows it has received the data from master properly . I said if it had got the 8bits of data it will acknowledge . In UART it will have a stop bit to find . How it happens in I2c?

Ihave already searched net for those questions . I believe its straightforward . I want some analytical and technical questions on these three protocols

Thanks in advance