"What did Jesus write on the Ground at John 8:6".
The short answer is that He wrote "Where is the man?", this is of course pure speculation, but all the facts indicate that this is the most likely answer.
This was a put up job to trap Him. The testimony of two witnesses was required to secure a conviction.
The unspoken words of the teachers of the law were "We don't need two witnesses, as this woman was caught in the very act".
Read Leviticus Ch 20 v 10. "Both the adulterer and the adulteress shall be put to death" The problem with this approach is that if you have caught her, then you have also caught him. So "where is the man?". Our Lords words show that He knew full well that the whole thing was a put up job,
He then bends down again, ie is no longer looking straight at them, and by averting His gaze, makes it easier for them to depart unnoticed as it were. This is indicated by His remarks to the woman "Where are they" when He knew full where they were.
Now we come to one of those rare occasions when the NIV translation is superior to other Bible versions, most read "Go away and sin no more" but NIV says "Go and from now on sin no more" which clearly indicates that this poor woman was nothing more than a common prostitute, who the teachers of the law were prepared to use in order to trap Jesus regardless of what her fate might be.
In all probability the scribes and Pharisees had instructed one of their man servants to go to the prostitutes house, they would then wait a short while before rushing in to arrest her in the very act, but in the confusion allow him to escape, as it was only her they wanted.