The Dwarves of the Iron Garrison plan to combat the denizens of Shakhajât in the Pit of Stonejaws.
'If we are to advance from Máttugard, we will need to do something about the city the Orcs have established here. Shakhajât, it is called, and long has it stood among the broken teeth of the Pit of Stonejaws. It was here that Bolg mustered the force that met its end before the gates of the Lonely Mountain in the Battle of Five Armies, but I do not know what it is like within its walls today.
'We need to draw the attention of its defenders so some of us can get inside and cause some trouble! Who volunteers? Imák? Bróin? Will the two of you blast a great signal upon horns of battle, drawing forth the hobgoblins that reside within the city?'
Bósi has asked Imák and Bróin to draw the defenders of Shakhajât out into the open.
Bósi is outside Shakhajât. Given Bróin's discomfort with the plan, perhaps you should volunteer in his stead?
Bósi has agreed that you can carry out Bróin's part of the plan: climbing either the left or right slope around the fortress and using a discarded horn of battle to draw forth some of the hobgoblins from Shakhajât.
Now that you have carried out your part of the plan, you should join the dwarves inside Shakhajât.
Bróin has seen a dwarf-woman fighting in the fortress and wants you to check on her while you combat the forces inside Shakhajât.
The dwarves have made their presence known to Bósi's satisfaction and are now ready to meet up outside Shakhajât.