Which one of the coordinate pairs represents the satellite orbit in the skyplot of the GNSS constellations?
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A skyplot is drawn in the local horizon system centered on the receiver, think about which two angles, one vertical and one horizontal, define a direction in that system.
Step 1: Set up the local horizon frame. At any receiver point on the Earth's surface, define a local frame with the horizontal plane tangent to the Earth's surface (the local horizon) and the vertical line through the receiver pointing to the local zenith. Any satellite visible in the sky can be located in this frame using exactly two angles measured from the observer.
Step 2: Name the two angles. The first is the elevation angle $E$, the vertical angle between the local horizon and the line of sight to the satellite ($E=0^\circ$ at the horizon, $E=90^\circ$ straight up). The second is the azimuth angle $A$, the horizontal angle between true north and the projection of the line of sight onto the horizontal plane, measured clockwise ($A$ from $0^\circ$ to $360^\circ$). Together $(E, A)$ completely fix the direction from the receiver to any satellite at any instant, and plotting $A$ around the circumference and $E$ along the radius (inverted so $90^\circ$ is at the center) generates the familiar skyplot arcs of each satellite's pass.
Step 3: Why the other pairs fail. Right ascension and declination fix a direction on the celestial sphere relative to the Earth's rotation axis and the vernal equinox point, this equatorial frame is used for cataloguing stars, not for describing a direction as seen from a specific point on the ground, so it is not what a receiver-centered skyplot uses. Altitude and declination combine one horizon-frame term with one equatorial-frame term, since these two terms are not defined in the same reference frame this pairing does not correspond to any standard coordinate system. Zenith angle only differs from elevation by a fixed offset of $90^\circ$, so while geometrically related, it is elevation, not zenith angle, that together with azimuth is the standard named pair for the horizon system.
Step 4: Conclusion. The satellite orbit traced on a GNSS skyplot is represented using the local horizon system coordinates, elevation and azimuth.
