STM32F429 I2C problem
Yes. 

The ST Micro STM32F429 datasheet says it has three I2C peripherals, so as long as the pins are available, you can connect them together, and use one as a master and the other as a slave.

If the pins of all three I2C peripherals are available, you could connect all three, and do a bunch of experiments to learn how to use I2C in multi-slave and multi-master configurations.

You should be quite careful about how interrupts are used. However, you can probably ignore using more than one interrupt, and still learn a lot.

There is an STM32F429-Discovery development board. If you are using that there are libraries to drive the peripherals. One is the older CMSIS-based STM32F429-Discovery Firmware, another is STM32CubeF4. 

There are a bunch of low cost I2C slave devices. As suggested in the comments, there are I2C EEPROM chips, and I've used low-cost I2C temperature sensors (under one GCP), to test software.