It is not easy to know "who invented the numbers on the clock". The way to measure time has existed since many years ago, but before the Middle Ages, only a small portion of the population was able to read and write, so probably they could not read the numbers on a clock as we do it nowadays.

The first clocks similar to the ones we have today had Roman numbers on their faces, but these numbers were replaced by the Arabic numbers that we use in our clocks today (1 to 12). The Roman numbers originated in ancient Rome, approximately 1000BC.

Looking at the history of timekeeping devices, we can notice that the first mechanical clocks, were invented in Europe at around the start of the 14th century, and they they had Roman numbers on their faces. So, we could say that it was around this time that the numbers on the clock were "invented" if we think of clock faces similar to the ones we use nowadays.

Wikipedia has a interesting article on this topic, you can read it or you can ask for help from your teacher, from ScienceLine, or from a grown up, in order to enjoy the article here.