heard it in Shameless. Someone said "Comprendo? Dekko?" pronouncing both with a rising intonation. I did research on "dekko" and found out it means "to look". Am I to assume that in this case like "comprendo" it means something like "Understand?See?"
When I was a kid living in Lancashire, not far from Manchester, it was always 'have a dekko' - "Have a dekko at that girl across the street!" Are you sure that's the sense here? Could Dekko possibly be a character? Of course, I'd have to hear to say for sure.
'Have a shufti' is another slang expression with the same meaning. I'd certainly notice if someone used either expression because I don't think they're that common these days, especially 'have a dekko', which I doubt I've heard since my youth. Or maybe I don't hear them because I'm no longer 18 and don't use slang that much anymore.
Interestingly, both terms were brought home by the English army, dekko (from Hindi) in the late 19th century and shufti (from Arabic) in WWII.