Both Mehri wēda and Akkadian wadū (variant of idū) make it uncertain whether it's appropriate to reconstruct *w- or *y- as the first radical of the Proto-Semitic (PSem) triliteral meaning “to know”.
Considering the Proto-Indo-European (PIE) root *weid-, it's just too tempting to wonder if there's a connection. If the original PSem root had *w-, then it would predictably become *y- in Western Semitic languages as is the case with other Iw-verbs like *wθb “to sit”.
The question is: What, if any, PSem form can plausibly account for the semantics and phonetics of the PIE root if this was indeed a Neolithic loanword? So I've been consulting a handy pdf called Semitic Binyanim for a hint at a sturdy answer. One form that may fit could be the active G-stem participle which is reconstructed to be of the vocalic structure of CāCiC-. So in theory, I'd then expect *wādiʕ- “knowing” and this would be one option to explain the PIE root, if correctly formed that is, since PSem *ā appears to correlate with PIE *ei also in the equation of PSem *θalāθi = PIE *treis “three”. I really need to find an in-depth book on Proto-Semitic grammar though...
 Bibliographic Bulletin (1982), University of Virginia, p.193 (see link).