How did Superman know that Lois was falling to catch her in time?
When Lex Luthor pushed Lois Lane from the roof in Batman v Superman: Dawn of Justice he may not have been worried about Lois dying and taken a chance in pushing her.
But how did Superman know that Lois was falling to catch her in time?
He knew, once he heard her screams
Superman can hear up to 500,000 Hz and has the best hearing, that we know of, in the DCEU according to this video:
How Powerful is DCEU Superman
As noted in the video Superman has the ability to hear everything up to approximately 1400 miles.
Once he heard Lois' screams, he used his 2,656,735 mph potential top flight speed (source) to fly from Kansas to catch her.