Is it forbidden to include the formula of invoking blessings upon our master Muhammad, peace and blessings be upon him, with God Almighty, after the saying, "So invoke not anyone along with Allah"? And is it forbidden to interpret the name "Dhakir" and attribute it to God Almighty?

The authenticity or error of the mentioned supplication (du'a) formula attributed to the Prophet, peace and blessings be upon him, cannot be confirmed without knowing its details. Generally, supplicating to other than Allah regarding matters that none but Allah can accomplish is major shirk (polytheism). As for applying the name "Dhakir" (The Rememberer/The Mentioner) to Allah, it requires evidence, because the names of Allah are tawqifiyyah (restricted to what has been revealed). However, it is permissible to use it as an descriptive attribute for Allah if the meaning is correct, such as "Indeed, Allah is the rememberer of those who remember Him," as reported from Al-Rabi' ibn Anas.