What does the open circle in the circuit depict?
A circle on a logic input means that the 'logic' is inverted. In this case pin 13 is the clock enable and it needs to be pulled low to enable the clock input (pin 14).


  Also does the pin 5 in 555 need to be connected to pin 12 in 4017?


CTRL    Provides "control" access to the internal voltage divider (by default, 2/3 VCC). See Wikipedia, 555 timer.

No, it doesn't get connected to pin 12 on the 4017. That's used if you want more than ten stages on the counter and pin 12 passes the data to the next 4017 chip.