You generate it here https://www.irs.gov/pub/irs-pdf/f8843.pdf
Form 8843 is not for Form 1040-NR, it is an information return for certifying one's exempt individual status.
Of course Form 8843 IS for 1040NR... It says so in the instructions of Form 8843...
You do not understand. F.8843 is a separate requirement from F.1040-NR.
Sure... If you need to file 1040NR/1040NR-EZ, file your Form 8843 with it. If not, file Form 8843 alone.
And of course you don't file Form 8843 if you are not excluding days for the substantial presence test.