EE-Student Electronics problem ( Diodes)
To know what the voltage across the diode is, you need to know the type of diode.  Is it a schottky or a standard silicon diode etc.?
Also, there is the &quot;rule of thumb&quot; voltage drop of  a diode and then there is the (more accurate) forward drop due to the amount of current flowing through it, which is given in the datasheet for the specific diode in question.
Lastly, your equation for calculating the current is missing a voltage.


I don't know how to find the voltage of D11

From physics, if two elements are in parallel, what is the voltage across them?