search for happiness. {sisku lo selgleki} or {sisku lo ka selgleki}?
Which translation is correct?
The second one, but probably not for the reasons you'd think.
{sisku} works like this: the x2 is a predicate that every element in the x3 is matched against; the x1 does the matching, whatever that means. By that logic, the sisku2 is a property of the sisku3, meaning that its ce'u-place refers to an element of sisku3.
With this definition, we can easily create a predicate meaning "to look for properties that make you happy", e.g. {.i mi sisku lo ka mi gleki ce'u}.
Similarly, if you're looking for a green shirt: {.i mi sisku lo ka ce'u crino kei lo[']i creka} -> "Of the shirts, I search for the green one(s)".
If we're looking for a particular thing, we have to resort to the use of {me} or {mintu}, depending on the case, in order to introduce a context-dependent variable: {.i mi sisku lo ka ce'u mintu lo crino kei lo[']i creka} -> "Of the shirts, I search for the green one(s)".
I don't know how to reflect the difference in English.
Now that we understand sisku, let's look at the real problem: what does it even mean to search for happiness? This question is philosophical to a ridiculous degree, so your mileage may vary. If it means "to do things that make you happy", then the translation is simply {zukte lo [da'i] selgei}, in which case the concept of "looking for" is completely out of the picture. If it means "to try to be happy about life/experiences", then it is simply {troci lo ka gleki lo selfri}; again, "looking for" is out of the picture.
This leads me to believe that the concept of "searching for immaterial things" doesn't even make sense. However, but assuming it does, does searching for properties that upon having them, you are happy, make you happy? Does searching for something imply that you obtain the sought-after thing? If it does, once you've "found" properties such that having them makes you happy, do you have those properties?
In sum, it seems to me like this is just another thing "that you wouldn't ever really say in Lojban".
.i mi'e la tsani mu'o