What is etymology Edit
Etymology is the study of the origin of words, for example the modern English word "today" from the on-line etymological dictionary
" O.E. todæge, to dæge "on (the) day," from to "at, on" (see to) + dæge, dative of dæg "day." Generally written as two words until 16c., after which it usually was written to-day until early 20c. Similar constructions exist in other Gmc. languages (cf. Du. van daag "from-day," Dan., Swed. i dag "in day"). Ger. heute is from O.H.G. hiutu, from P.Gmc. *hiu tagu "on (this) day," with first element from PIE pronomial stem *ki-, represented by L. cis "on this side." "
It might not be too far to say that some words in a conlang will not have an etymology, but doubtless most will. All of the words in esperanto are taken from another language, so all of them will share most of their etymology with the root. so kiso comes from the english kiss, and shares the rest of that words etymology.
In another conlang, Jorayn, the word dufadufath, meaning deer has the etymology that follows
"Imitative of the sound made by a deer's feet as they fall upon the freshly rained upon earth of the forest floor"
So the etymology might be more complex, such as that of Tolkien, who had the Quendian language family.
above is a chart tracing the etymology of the word for people
kwendī -> pendi -> penni
If you want to have full etymologies for your language it would be best to have it evolve from a proto-language, following sound changes and lexical shifts along the way.