I am not sure whence this word originates, it sounds like something the British took home from India. It means to look at and, sort of, assess/absorb something. It is widely used in Ireland and the UK
'If you bring your new work along this evening I'll take a dekko at it'
Yes, its actually a word derived from Hindi (Indian language). Basically 'dekh' means to look and when you say 'dekho' its asking someone to take a look.
Yeh ladki ko dekho- Look at this girl
In English slang
Give that girl a dekko