Which electrode is used to measure the electrode potential of any electrode?

If the electrode potential of $Zn^{2+} | Zn$ is $-0.76 \, V$ and the potential of $Cu^{2+} | Cu$ is $0.34 \, V$,what will be the $EMF$ of the cell formed by both electrodes in $V$?

The standard reduction potential for $Mg^{2+}/Mg$ is $-2.37 \ V$ and for $Cu^{2+}/Cu$ is $0.337 \ V$. The $E^{\circ}_{cell}$ for the following reaction is $Mg + Cu^{2+} \longrightarrow Mg^{2+} + Cu$

For a closed circuit Daniell cell, which of the following plots is the accurate one at a given temperature?

Two half-cell reactions are given below:
$Co^{3+} + e^- \rightarrow Co^{2+}, E^{\circ}_{Co^{3+}/Co^{2+}} = 1.81 \, V$
$Al^{3+} + 3e^- \rightarrow Al(s), E^{\circ}_{Al^{3+}/Al} = -1.66 \, V$
The standard $EMF$ of a cell with a feasible redox reaction will be:

Arrange the following metals in the order of their decreasing standard electrode potential: $Mg, K, Ba, Ca$.