No dudo + subjunctive

Question

Hi, do you have a lesson anywhere that addresses when the subjunctive or indicative is used after constructions like “no dudo que” I was taught they required the indicative, but an example in another lesson called for the subjunctive, and when I searched online I found a lot of personal opinions, but not a good authoritative source. Thanks!

Here is your example from a Kwiziq that prompted me to research more:

No dudo que ________un buen lugar para celebrar la boda. I don't doubt you will choose a good place to celebrate the wedding.HINT: Conjugate the vosotros form of "elegir" in El Presente Subjuntivo.

Answer

Hola A,
sentences using "no dudo que..." always bring lots of comments and different opinions. There are two ways to see "no dudo que...":
1. when we are simply saying that "we are sure about something". In this case, as a certainty we use the indicative, for example:

No dudo que aprobarás el examen.
I am sure you will pass the exam.

2. when someone says something, and then we reply to what was said with "no dudo que... + subjunctive". For example, imagine someone says:
No te preocupes, mi novio es un buen manitas y lo arreglará.
(Don't worry, my boyfriend is a good handyman and he will fix it.)
Then the other speaker replies to that saying:

No dudo que tu novio sea un buen manitas, pero creo que necesitamos a un experto para arreglar esto.
I don't doubt your boyfriend is [~might be] a good handyman, but I think we need an expert to fix this.)

In this last sentence using "no dudo que... +subjunctive" we are neither confirming nor negating what was said previously, but somehow, with the subjunctive it leaves a bit of room for doubt. It is as if the second speaker was "detaching" himself/herself from that previous statement. 
In this second context , in my opinion, is when "no dudo que" is more commonly used, therefore it is more common to see the subjunctive after no dudo que. 
If we wanted to say "I am sure that..." (point 1, with the indicative) I think, instead of using "no dudo que..." we'd probably say this same thing saying "Estoy seguro/a de que... + indicative" or "Sé que... + indicative". 
I agree, though, that this lesson needs an extra point to talk about this difference or a new lesson all together, so that is noted. 
I hope this clarified it.
Saludos
Inma