Are these 2 sentences equivalent?

wholegrainHe's a loner, isn't he?

He's a loner—isn't he?

The first sentence is fine.

I would definitely use the comma rather than the dash, if asking for confirmation (?) or making an exclamation (!). The only exception would be if the writer specifically wanted to indicate a longer pause in the speaker's line.

Can you ascertain it?

Because doesn't a dash at the end of a sentence equals to two parenthesis?

wholegrainCan you ascertain it?

Because doesn't a dash at the end of a sentence equals to two parenthesis? NO

You need a comma, not a dash.

Sources?

I just want to make sure.

You're well, aren't you?

The weather is wonderful, isn't it?

(The Right Word at the Right Time)

No, cite me the sources where you found the rules upon which you based to affirm what you did.

I'm fond of the online writing lab at Purdue: http://owl.english.purdue.edu/handouts/grammar/g_overvw.html

Ok, thanks.

The following is provided by an English language teacher from the British Council. I am right, aren't I?
You have to go, don't you?
I have been answering, haven't I?
No