How do you convert 8.41 g/ml to kg/l ?

First of all u need to be aware of the representation values of 1 milli and 1 kilo:
milli(m) = 1/10^3 = 0.001
kilo(k) = 10^3 = 1000

so, mL to L,
8.41 * g/ml
= 8.41 g/mL / 1000 mL
= 0.00841 g/L

to convert g to kg we have,
g = 10^3 * (1/10^3) * g
= (1/10^3) * kg

therefore, 
0.00841 g/L / 1000 g
= 0.00000841 kg/L

The final answer is 0.00000841 kg/L