Are the German words wer "who" / was "what" derived from the question word wo "where" + pronouns er "he" / es "it":
- by analogy with the Old Slavonic [which could inherited this thing (feature) from the Greek, whereas the German languages could inherited this thing (feature) from the Latin, whereas the Latin language could inherited this thing (feature) also from the Greek], wherein words кои (koi) “who” / что (chto) “what” are derived from the pronouns и (i) "he" / то (to) "it".
Note: The non-slavonic speakers may pass by this part.
The Old Slavonic has two third-person singular pronouns, the masculine и (i) "he" and the neuter то (to) "it". The Old Slavonic also has the word къ
де (k' de) means "where", where де (de) is the Old Slavonic suffics да (da), which is used to form a noun/adverb from the short (indefinite) adjective къ(k') by analogy whith the English suffics "th" long/length: правъ (prav') "adj. right" + да (da) = правда (pravda) "truth", кривъ (kriv') "crooked" + да (da) = кривда (krivda) "falseness", вьсь (v's') "adj. all" + де (de) = вьсьде (v's'de) "everywhere", съ (s') + де (de) = съде (s'de) "here" and so on***. The ending alternation is the result of declension (the Old Slavonic has grammatical cases).
The transformation of the letter ъ (') to the letter о (o) is caused by its new position in the word. In the old word къде (k'de) the ъ (') letter was not stressed (weak position) but now it is stressed (strong position). As a result, the Old Slavonic letter ъ (') in our days in some words transformed into the Russian letter "o" and in the other words it is completely disappeared.
*** онъ (on') + де (de) = онде (onde), инъ (in') + де (de) = инде (inde), овъ + де (de) = овде (ovde).
- by analogy with the Latin words quis “who” / quid “what” that could be derived from the question word quo “where” + pronouns (demonstratives), the masculine is “he” and the neuter id “it”.