Must one whose repentance from abandoning prayer due to watching pornography has been repeated pronounce the Two Testimonies and perform ghusl each time, or is there another action for his sincere repentance?

Intentionally abandoning prayer is a grave sin. Some scholars have gone so far as to consider one who abandons it to be an apostate, outside the fold of Islam, while the majority of scholars hold that such a person is among the most wicked of people and in grave danger, but not an apostate in a way that removes them from the fold of Islam.

You must repent to Allah Almighty for abandoning prayer. You are not required to renew your Islam, according to the opinion of the majority of scholars. You are obligated to make up the prayers you intentionally missed, according to the view of the Four Imams and the majority of their followers, because they are a debt upon you. However, some scholars, such as Ibn Hazm and Ibn Taymiyyah, believe that these prayers do not need to be made up due to a lack of evidence. The adopted fatwa (definition) is the opinion of the majority, as it is more cautious and absolves one's responsibility. Calculate all the prayers you missed and make them up according to your ability.