What is the voltage across the current source in the following figure assuming ideal sources?

We have redrawn the circuit by taking the potential as Vs across the current source & V_A across the 12 Ω resistance.

Applying KCL at node A

The net current flowing into the A terminal will equal the net current flowing out of the terminal.

2 = 1 + \(\frac{V_A -6}{6}\)

⇒V_A = 12 V

We know that the current flowing across the 1Ω resistance is 2 A.

\(\frac{V_S - V_A}{1} = 2 \)

⇒ Vs =  14 V

Thus the voltage across the current source is 14 V