Do RGB conversion to CIE XYZ and define value ?

I need to do computation in CIE XYZ, so I do RGB conversion to CIE XYZ. Since we can’t define color value in XYZ like we do in RGB, in CIE XYZ how exactly do I get value of the line spectrum color (color on the line) ? or any line within the gamut ?

CIE XYZ :
14