lox is a kind of smoked salmon, from Yiddish לאַקס laks, from Old High German lahs "salmon". The Proto-Indo-European root is *laḱs- "salmon". The IEW has laḱ- 653 "to be spotted, salmon".
lakh/lac/lack is Anglo-Indian for "one hundred thousand", from Hindi लाख lākh, related to Sanskrit लक्ष lakṣa "one hundred thousand", also "mark, sign, token". Hobson-Jobson says the word has been borrowed into Southeast Asian languages like Malay and Javanese.
Pokorny derives Sanskrit lakṣa from *laḱ-; the sense development is presumably something like "spotted > lots of marks > a vast amount like one hundred thousand".
There is a homophonous Hindi word लाख lākh "gum-lac, a kind of wax formed by the Coccus lacca" (a scale insect that feeds on certain trees in south Asia). This is related to Sanskrit लाक्ष lākṣa "a kind of red dye", which is also possibly from *laḱs- (because salmon are red?). The Hindi word found its way to French as laque en écailles, which was calqued into English as shellac, that is, "shell-lac" - lac that has been melted and run into thin plates (OED).