Denote means either to define something exactly, as in its dictionary definition, or to be represented by a symbol - the red dress denotes danger, whereas to connote is to imply - just like giving a hint, or suggesting, without being explicit.
An example could be: summertime denotes a season of the year, whilst it connotes warm weather/holidays. So we could say summer has connotations of hot weather and holidays.
Credits:
Created with images by slavikfi - "las-palmas gran canaria canary islands"