King Porus surely spoke Punjabi since he was a Punjabi (from Pakistani Punjab) but the language he spoke was the ancient Punjabi. As for the alphabets ਧ ਢ ਭ, these have been there for as long as Punjabi has been there. Guru Sahib just gave these sounds the alphabets. Guru Sahib gave us the Gurmukhi lipi. Before Gurmukhi, there were some other scripts used for writing Punjabi and with the advent of Muslims, Punjabi was also written in Shahmukhi script (Arabic script) but by far, the most suited script for writing Punjabi is Gurmukhi.
Kulbir Singh