If i invest, then is there any chance to loss all the money?
yes there is a chance for you to get loss all the money so if you want to invest in cloud mining better you search first before you invest.
If i invest, then what should be the amount first?
the amount is depend on how much you are ready if one day the cloud mining site is scam so you don't regret for investing in that site.
And in which sites would be better to do mining?
in my opinion, genesis mining, hashnest is still legit but i don't know about their future, they can scam you too because there no company that will stay forever and you should know. at least, i get ROI in that site.
from all of this, i think its better for you to learning trading like above me said or you can buy bitcoin and altcoin and then hold it for a year. but for me, i'd better to do trading because this is my chance to increase my bitcoin.