I2C concept and Working
It may depend on the chip. Do you have a datasheet?

Here is a drawing I made recently (I2C HDMI encoder) :




A : Chip address
R : Register number
D : Data read/write
Blue : Host signal
Red  : Target signal


The number of bytes is determined by the stop condition on writes and the ACK level for reads (ACK=1 : Lst byte).