It depends on:

where are you originating
are you flying early or late december
are you skywards members (preferably silver or gold?)

If you are connecting in Dubai, the chances on the second sector / both sectors are slim to none. If the first sector is usually full in economy with seats in business you can ask if they can move you. If you are travelling during peak christmas time on a routr such as MAN-DXB, it is unlikely that any J seats will be free.

Cheers