Sorry, but without having such an MCU or a board, there is not much I can do myself.
However, what I would check:
The peripheral pins require appropriate initialisation, i.e. enabling the port & pin, and switch it to the correct peripheral mode (I2C in this case). In the LPCXpresso SDK, this is done in a file called pin_mux.c. Check those are correct for your MCU and your board, cross-referencing with the datasheet (port/pin assignment).
For test purposes, you could also initialize it to standard push/pull GPIO, and toggle it in your code. That should be visible on a scope.
Second, check the board schematics the pin is really usable for this purpose, and not blocked by other attached components.
And third, check schematics and the physical board that a pull-up resistor is present on both I2C pins. Without such a pull-up resistor, you cannot measure a signal on an open-drain output.