What wavelengths(dominant) the primary RGB colors are supposed to be in sRGB color space in nanometers?
The primaries of sRGB are not pure wavelengths, they are color mixtures. Their true definition is in terms of CIE chromaticity coordinates. That said, for sRGB, the red primary is close-ish to 610nm, green is very roughly 555nm, and blue is close-ish to 465nm.
The Rec. 2020 RGB space, by the way, is actually defined using pure wavelengths for the primaries: R=630nm, G=532nm, and B=467nm.