It's your turn, you haven't activated Nicol Bolas, Planeswalker. (His loyalty = 3 atm)
Your opponent uses Lightning Bolt at instant speed.
You can then activate Nicol Bolas, Planeswalker in response to his instant spell. You have priority being your turn, which means that whilst a planeswalker ability is normally sorcery speed you can respond to a spell by adding his ability to the 'stack'
Just for the record : this is TOTALLY INCORRECT.
You CANNOT activate a Planeswalker in response to a spell or ability.
Planeswalker abilities have to be played as Sorceries, which means the stack has to be EMPTY.
To play this correctly :
The
Nicol Bolas player has Initiative, so there's NO WAY the other player can play a
Lightning Bolt BEFORE the initiative player had a chance to activate his Planeswalker and thus tick him up and put the ability on the stack.
If the initiative player played another spell or ablility though, which allows the opposing player to react to it, then he can play his
Lightning Bolt alright and it's TOO LATE for the Planeswalker to activate as the stack has to empty for that.
Another way to remember this : a Planeswalker CANNOT REACT to a spell or ability, his/her ability always has to be the FIRST on the stack.