Translation:I do not know which tools they make it with.
I got this right with "I don't know which tools they make THEM with," but I'm wondering why the translation shown here uses "make IT with"...?
Je is the accusative (one of more forms) of ono http://prirucka.ujc.cas.cz/?id=ono&dotaz=je&ascii=0
Thanks a lot for that link! The table perfectly explains why I never could find a system in those forms… Are all those alternative forms used interchangeably, or only in certain situations?
Not at all. The "n..." forms are used with prepositions. Then out of "ho, je, jej" the by far most common is "ho". The other ones are bookish and that's why I would, as BoneheadBass did, normally first think that it is in plural (them). The possibility of neuter singular comes to my only after thinking more about it.
The textbook "New Czech Step by Step" p.227 differentiates 3 types of pronoun here. What do you think of this? (1) weak/short (can only be in 2nd position): ho (2) strong/long (can be in any position, emphasizes the meaning of the pronoun): je (and "jej" I guess) (3) prepositional (follows prepositions): ně, něj
Yes, that's the same I wrote. But I add that the je/jej is quite bookish and not used in common speech.