Okay, well, that's a dumb design.

Anyhow, the diode needs to go across whichever button activates the doorbell. If the top button is normally your button, then the diode goes across the two terminals on the top button.

Diodes are directional, and we have no way of knowing which wire is which in that tangled mess, so if it doesn't work one way, turn the diode around.

I can't really tell what's going on there. If you've got more than one doorbell operated from the same button (ie, you push the button, and it "rings" at two different locations), the second one may be causing some electrical confusion.

You should have or get or make a simple diode checker.
A diode is really simple. If you put voltage across it with
neg and pos one way you'll see electricty flowing through
the diode. If you turn the connections around you won't see any electricty.

Compare that with a light bulb. No matter if you put the wires one or the other way the bulb lights.

So the only resort if neither try works for you is to check
the diode that it's working. It's simple. You put a meter with one lead there and theothe lead over there. IF you see a signal then you swap the leads. This time you should not see a signal. It works one way.

What woudl you think if you saw a signal no matter which way you put the meter leads? The diode would be broken.
You would have to replace it.

What would happen if no matter which way you put the meter leads and you got no reading or signal from your
test? The diode would be broken. You would have to replace it.

The reason you don't just replace it is this:

It's poor logical thinking. It's better to prove that it's
broken so that when you put in a new one and the new
one does not work either.. then you know something
else is ALSO wrong.

So

1. Get a meter for $10 at Sears or Harbor Freight. It will
be worth it for later. Learn to use it. It's acutally fun.

2. Check the diode. You can find online how to use your
meter to test the diode. When you're at the shop where
you buy the meter take your diode with you if you
can. If you can't then try to buy one that is approximately
the same physical size. AT least it will fit mechanically.
For specifications they're simple. They are usually rated
at the highest current. 1 amp is typical for this kind
of application. IF you hve an old door bell with a ringer
and buzzer then get a 2 or 3 amp if possible. If it's
electronic than anything should be OK. But get 1 amp
if possible. The other spec, the voltage should be 100 volts
or more. They're all this or more so no worry.

3. Test the diode. Two ways to try it. One way, then the
otehr. It shold be opposite readings each way. Test the
good one, first, instead. It, if it's good, will show you
how the diode works. The meter puts voltage into the
diode. When the diode lets electricity through the meter
then the meter reads a signal. If the diode blocks the
signal from getting through the meter then
the meter reads nothing, 0.00 .

So you've got a whole 2 weeks of electronics training in
3 paragraphs and 10 minutes.

Try the diode one way, if it works you're done. If not
try it the other way. If it works. .. etc. If it does not
work either way then
A. Check the diode again to be sure it's still OK. If not
then you have a different problem It's nearly 100% sure
it will be OK.

B. If it doesn't work and diode is OK then get sommme more advice from only or here. You might not be
getting DC or AC voltage from the bell's transformer.
We'll be guessing at that point.

I'll check back to see how you're doing
Andre

ps. I did just see you might have more than one door bell and that might mean more than one diode.

What you might think to try but you'll have to figure it
out is this:

make one door bell always on or always off. This will allow
just 1 button to operate the door bell. One you verify
that button works. Then swap the idea the other way.
Make the one a push button and force the push button
to always be on , or off, so that now the other button is
the only one that makes the bell work Now you've verified
the buttons work and that you have power.

There's an easy way to test but you'll learn more and its'
better to make both buttons work without the other
to test things. Now you add diode(s) .

At this point , I think, you have to put both in the circuit
to make the system work. You'll have 4 choices.

That is if you have 2 buttons and 2 diodes. Each diode can
go one way or the other. And the other can go one way
or the other. You try one , one way. Then try it the other.
You leave it alone try the other one way, then the other.
When you're done you will have tried the diodes in
4 diiferent connections .

You should look up online a '"dual doorbell" wiring diagram.

You can go to Leviton site and look at their doorbells as
they might have some drawings which you can follow.

If no Leviton then another company. Try Amazon.com for
other doorbell names.

Good luck

Oh boy.

OP lives in a multi-unit building. Only one of those buttons is his, and he should only be worried about the top one.

He does not need two diodes, in any case. The electronic doorbell he has requires power even when it is not "ringing", so the diode allows one half of the AC cycle to flow through for that purpose, while the other half flows through only when the button is pressed. The electronics sense the presence/absence of the second half and decide whether or not to "ring" accordingly.

If it is not working, then either the diode is backwards, or the power source is DC.