[General] came to know/ knew/ learnt /found out

[beesting]

Suppose, today I had a conversation with my friend, in the night. The friend won't be doing his home work due for tomorrow. I came to know of this today morning.

Which of the following is correct?
1. Today only I knew that you aren't doing the home work.
2. Today only I learnt that you aren't doing the home work.
3. Today only I came to know that you aren't doing the home work.
4. Today only I found out that you aren't doing the home work.

This is not an exam question. So there would definitely be much better sounding options. But I would specifically like to know the acceptability of above sentences.
I realize "Only today I ...." should be the word order to get the above point across correctly. That otherwise it could mean "only I(and nobody else) knew". But in a casual conversation with a friend, is it natural or normal for a native speaker to say it as "Today only I"(in the given context)

I have heard the song "If only I knew what I know today"- Christina Aguilera, and the placement of "only" looks similar to the one I did first.

 

[MikeNewYork]

Suppose, today I had a conversation with my friend, in the night. The friend won't be doing his home work due for tomorrow. I came to know of this today morning.

Which of the following is correct?
1. Today only I knew that you aren't doing the home work.
2. Today only I learnt that you aren't doing the home work.
3. Today only I came to know that you aren't doing the home work.
4. Today only I found out that you aren't doing the home work.

This is not an exam question. So there would definitely be much better sounding options. But I would specifically like to know the acceptability of above sentences.
I realize "Only today I ...." should be the word order to get the above point across correctly. That otherwise it could mean "only I(and nobody else) knew". But in a casual conversation with a friend, is it natural or normal for a native speaker to say it as "Today only I"(in the given context)

I have heard the song "If only I knew what I know today"- Christina Aguilera, and the placement of "only" looks similar to the one I did first.

I don't find your uses of "Today only" to be natural. In addition, the verb "knew" in the first doesn't work for me. Also we don't use "today morning".

 

[Barb_D]

Only today did I learn that you have not been doing your homework.

 

[Raymott]

As above, or 'find out' or 'discover'. Don't use 'know' for this. It's a common error.

 

[beesting]

As above, or 'find out' or 'discover'. Don't use 'know' for this. It's a common error.

Did you mean, "know" can't be used if we are saying it like Barb_D suggested? Does that have anything to do with the context I have provided, or is the sequence "Only today did I know"? always wrong?

 

[Barb_D]

Did you mean, "know" can't be used if we are saying it like Barb_D suggested? Does that have anything to do with the context I have provided, or is the sequence "Only today did I know"? always wrong?

"Knowing" something is a state.
"Learning" (or "finding out," or "discovering" or even "coming to know") are events/activities.

These are possible:
I knew about it only after you told me. I was unaware of it until then.
I only knew about the party after Mary let it slip. I was in the dark until just yesterday.
Only since yesterday have I known about it.

You could, if you really, really want to use "know" instead of learn, discover, find out, realize, etc. use "come to know." Only today did I come to know that.."

 

[Raymott]

Did you mean, "know" can't be used if we are saying it like Barb_D suggested? Does that have anything to do with the context I have provided, or is the sequence "Only today did I know"? always wrong?

I can't see where Barb had suggested how to use 'know' prior to her above post.
You can say "come to know" though it's not the most natural thing to say.
We don't say, "Only today did I know something." We says, "Only today did I find out/discover, etc. If you feel you have to use 'know' you can say "Only today did I come to know..." but it sounds a bit Dickensian to me.