referring to a possible future/referring to an unreal present

That's a tricky one, to be honest.
In a nutshell, if you're talking about something that you lack now or in general, this will normally change into an unreal-present-situation context where you can use an unreal past. So, because of your lacking the necessary knowledge to answer a question now, you can say If I knew (but I don't know) the answer, I would tell you. You can't do the same with your other example sentence, so you can assume that it will refer to a hypothetical (possible) situation in the future.

sb70012 said:

Future time:

1. Catherine: If I lost my job, I would be in serious trouble. (referring to a possible future situation)
Catherine said that if she lost her job, she would be in serious trouble. (the reported words are true; she might still lose her job)
Catherine said that if she had lost her job, she would have been in serious trouble. (the reported words are out-of-date; it's not possible that she will lose her job)

Present time:

2. Paul: If I knew the answer, I'd tell you. (referring to an unreal present situation)
Paul said that if he knew the answer, he'd tell us.

Hi,
I have problem understanding or comparing the red part with the blue part.
The structures are same. Is there any clue to recognize if it refers to future or present?
I mean:
Number 1 has used "lost" and number 2 has used "knew"
Number 1 has used "would" and number 2 has used "would"
How or from what aspect number 2 refers to present but number 1 refers to future?
Is there any clue to tell us which one refers to future and which one refers to present?
I see no difference between 1 and 2.
I mean the structures of number 1 and 2 are same.
Then why 1 refers to future but 2 refers to present?
How should we detect if it refers to present or future?
Both 1 and 2 have same structures then why 1 refers to future and 2 refers to present?

Source: http://www.grammaring.com/second-con...ndirect-speech
Thank you
​

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As engee said, these constructions are tricky.

Let's look at Catherine. She said to you "If I lost my job, I would be in serious trouble." She is currently working so she is not in serious trouble. If you report that as "Catherine said that if she lost her job, she would be in serious trouble", people will understand that she is still working and does not want to lose her job. If you backshift tenses to "Catherine said that if she had lost her job, she would have been in serious trouble",
people will believe that she did not lose her job and is no longer concerned. That would change the meaning. So we shouldn't backshift there.

Now, onto Paul. Paul said "If I knew the answer, I would (I'd) tell you." When Paul spoke to you in the present, he did not know the answer, so he couldn't tell you. This one could be backshifted to "Paul said that if he had known the answer, he would have told us." It means the same as the original: He did not know the answer at the time, so he couldn't tell you at the time. In this case, backshifting did not change the meaning. However, not backshifting also preserves the meaning: "Paul said that if he knew the answer, he would tell us." In this case, backshifting is optional. If the conversation about Paul happened shortly after Paul's statement, I would not backshift. If the conversation about Paul happened at a later time, I would probably backshift it. The issue of backshifting tenses in indirect speech is far more complex than is usually taught in ESL courses.

MikeNewYork said:

The issue of backshifting tenses in indirect speech is far more complex than is usually taught in ESL courses.

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I agree- it's not an automatic process and there are a number of factors to take into account.