To get line angle you can use field calculator depending what exactly you need:
- line_interpolate_angle(geometry,distance)
- angle_at_vertex(geometry,vertex)
For more details check help in field calculator: 
Result is in degrees, to convert it in grads you need to multiply by (400/360).
So field calculator expression would be something like: line_interpolate_angle($geometry,0) * (400 / 360)