Which text from "after twenty years" provides the best evidence that “silky bob” is surprised that his friend is now a policeman?

The line would be "Twenty years is a long time, but not long enough to change a man's nose from a Roman to a pug." With Silky Bob realizing that the man beside him is not his friend Jimmy Wells, this line expresses the surprise and distrust of Bob, and his impending fear of going to jail.