easy way to find the V7 of a target chord? build a V7 chord of the target chords chordal 5th. G7 is the V of cm,CMaj (C-Eb/E-"G").... B7 is the V of em/EMaj (E-G/G#-"B"), etc.
In minor keys it's really common to borrow the V7 from parallel major keys instead of v. That's the only reason I use it in the example. But you could use v here with no problem. I hope that helps.
You can also think about it being in harmonic minor, yes. It's a bit more complicated, I made a video about it if you want to learn more : ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-GAHPwLd4y48.html
Is it just me or in minor keys, secondary dominants can kinda resolve to the I chord too? For example, in D minor: if on guitar I'll play V/v E7 voiced as x7675x and next D minor voiced as x5774x. It feels like it kinda resolves (?). I like to end longer phrases like that when improvising chord progressions
If you take this formula of using 5 of 5 as an intermediary tonic and applying it to a 4 of 4, can you say that it will become a secondary subdominant? Ex in C Major, F is the 4th, count up a 4th, we get to Bb, which is a bVII. The same applies to a secondary mediant (3 of 3 is Ab), it becomes a bVI. Is this a thing, does it apply to others, or it's just for 5ths?
