See SQL commands that DBIx::Class is generating

Set environment variable:
    DBIC_TRACE=1

Pretty printing is available, as of DBIx::Class 0.08124:
    DBIC_TRACE_PROFILE=console DBIC_TRACE=1

(sources: CPAN docs, and a foolish manifesto blog)

For plain DBI calls, see also:
    DBI_TRACE=1

(source)