What three incidents concerning Ewell occur in chapter 27? From these incidents and from Atticus, what do we learn about Bob Ewell?

The three incidents to which you refer are: 1) Bob Ewell gets and loses a job because of his own nature and his ways but he blames his losing it on Atticus; 2) someone attempts to break into the house of the judge who presided over the court case, Judge Taylor (it's an obvious assumption that the person who attempted the break-in was Bob Ewell); 3) the Ewells throw stones at Helen Robinson when she walks by the Ewell house on her way to and from work at Link Deas which causes Deas to warn the Ewells to stop.  These events tell us what a petty, immature, vindictive, and dumb bully Bob Ewell is.  He was made to look foolish and he was shown for the lazy, abusive alcoholic that he is.  He did the things he did - blame Atticus, attempt the break-in, and harass Helen Robinson - as his way of getting back at and scaring those he feels wronged him.