It depends. A 50MHz or better dual trace delay timebase CRO can resolve I2C transfers well enough that you can pan through the data packet a byte at a time using the delay multiturn control, manually decoding it and writing down the result. However to do so you need to be able to generate a repeating data packet with stable timing, and preferably a separate signal to trigger on at the start of the packet. Without control of the master's firmware, if you are unlucky, you don't get to see much except a blur. You will be able to confirm logic levels and you *MAY* be able to roughly estimate the speed, but that's about it. OTOH if you are lucky and the master provides a lot of repeating bus activity (e.g frequently polling a sensor), you may be able to get a stable display of the first few bytes of the transfer that you can take measurements from and even decode.
With a single timebase CRO its a lot more difficult. It probably wont have a large enough holdoff range to stabilise the display without moving the variable timebase control from its calibrated position, which leaves you with the situation of being able to see some of the data but not being able to make time measurements.
TLDR: A CRO isn't the right tool for the job, use a logic analyser with I2C protocol decoder or a DSO.