Why does the verse ask about where lions stay?
Rashi: This is a lamentation about Ninveh, which used to be a dwelling for kings valiant and strong like lions.
Radak: So the nations will say when Ninveh is destroyed. It was a dwelling of lions - from it came men like lions who tear people of the world and bring the prey to Ninveh. It is a dwelling of lions "u'Mir'eh Hu la'Kefirim."
Malbim: The author turns to Beis ha'Melech, which is desolate. He is astounded at Sardanafal's cruelty - he burned his wives and children without mercy. Where is the palace where the kings dwelled - they are old lions.
Why does it add "u'Mir'eh Hu la'Kefirim"?
Malbim: Around the king's castle grazed the young lions - his children.
Why does it say "Asher Halach Arye Lavi Sham Gur Aryeh"?
Rashi citing Targum Yonasan: A place where kings went and left their children there, like a lion that dwells [on its prey] confidently.
Radak: All went there (even lion cubs) with their prey.
Malbim: The male and female lions (king and queen) went there with their small children. Radak - it is as if it says Arye v'Lavi. Sometimes the prefix Vov is omitted, e.g. "Shemesh Yare'ach" (Chabakuk 3:11).
What do we learn from "v'Ein Macharid"?
Radak: No one scares them.
Malbim: They were confident there.