In principle, I would think this plan could work, though it is not clear to me what the practical benefit would be
The show never reveals enough about the mechanics of a harsesis for us to know, but we can make some assumptions.
What does it mean to "contain all the knowledge of the Goa'uld"? Presumably, the child of Apophis and Amauanet contains either the knowledge of Apophis, the knowledge of Amaunet, or a combination of both. I think we can safely say that it does not contain knowledge from Heru-ur (e.g. disposition of Heru-ur's fleet). It doesn't fit the style of the rest of the show, where there is usually a good explanation (within the show's context) for everything. They're not above using psychic powers now and then (e.g. the hok'taur) but they don't bring in complete magic.
Since you can only obtain useful knowledge from at most one parent (the other is a Tokra and already knows what it knows), what is the procedure and what could you reasonably learn?
Well, "all you have to do" is grab a Goa'uld, establish the pregnancy, raise the child, and when the child grows up enough for you to question it, you may be able to extract some 5-10 year old intelligence about an enemy that knows what you did.
There doesn't appear to be any really old knowledge that would be useful to the tok'ra. They understand how the hyperdrives, shields, rings, stargates, staff weapons, etc work. So I think they could implement this plan, but it would have limited utility.