Is it sufficient to pour water on the spot where some menstrual blood has fallen to purify it, or is it necessary to recite the Two Testimonies when pouring water on it?

An impure place is purified by pure water, and there is no evidence for the legitimacy of uttering the word of Tawhid when purifying impurity. We have been legislated to say "I bear witness that there is no god but Allah, and that Muhammad is His servant and Messenger" after ablution, and not in every place merely because the word of Tawhid is the best of speech. Similarly, uttering "La ilaha illallah" a thousand times daily or saying it when carrying the deceased is an innovation, and it is not legislated to say anything instead of prostrating when reciting a verse of prostration if prostration is difficult, because that is an innovation.