The philosophy of Prabhupada and Gaudiya Vaishanva is Achintya Bhedabheda. (Inconceivable oneness and difference)
I've mentioned/listed it's overview in my answer on Dvaita vs Advaita vs Vishistadvaita vs Shuddhadvaita vs any other.
According to Achintya Bhedabheda, Brahman is simultaneously one with and different from his creation. The relationship between Brahman and Jivatman is like Sun and Sunshine. Qualitatively the Sun and the Sunshine are not different, but as quantities they are very different.
The verse mentioned in the question is about
tattvaṁ i.e Absolute Truth
yaj jñānam advayam means of which knowledge is non-dual.
Read the Purport:
As it is explained in the first śloka of the First Chapter of the Bhāgavatam, the Supreme Truth is self-sufficient, cognizant and free from the illusion of relativity. In the relative world the knower is different from the known, but in the Absolute Truth both the knower and the known are one and the same thing. In the relative world the knower is the living spirit or superior energy, whereas the known is inert matter or inferior energy. Therefore, there is a duality of inferior and superior energy, whereas in the absolute realm both the knower and the known are of the same superior energy. There are three kinds of energies of the supreme energetic. There is no difference between the energy and energetic, but there is a difference of quality of energies. The absolute realm and the living entities are of the same superior energy, but the material world is inferior energy. The living being in contact with the inferior energy is illusioned, thinking he belongs to the inferior energy. Therefore there is the sense of relativity in the material world. In the Absolute there is no such sense of difference between the knower and the known, and therefore everything there is absolute.
So, there is no difference between knower and known in the absolute that's why it is called non-dual.
You can refer alternative translation at CC Madhya 25.132:
“ ‘The Absolute Truth is known by the self-realized souls as a unified identity known by different names — impersonal Brahman, localized Paramātmā, and Bhagavān, the Supreme Personality of Godhead.’
Q. How to interpret this Advayam word for Bramhan. How what are Sri Vaishnava views/comments on this word.
If you're looking for Vishishtadvaita interpretation for Advayam, refer to similar question: How does Vishishtadvaita interpret "One without a second"?