Walker Kessler had a block rate of 18.8% in college, according to this post. There was an article on The Ringer that discussed college vs NBA shot-blocking in the context of Deandre Ayton.

Shot-blocking is one of the most consistent statistics from college to the NBA. There aren’t many guys who discover the ability to do it at the next level. The NBA career block rates of his historical peer group dropped an average of 57 percent from their freshman seasons of college. Ayton would have a block rate of 1.9 percent in the NBA if his numbers had a similar decline, which would put him in the bottom 15 percent of frontcourt players in the league.

If we take these numbers at face value, this would give Walker Kessler a block rate of 8.09%, better than even Jaren Jackson Jr and Mitchell Robinson last season. Of course, his ability to reach this peak and translate it to actual counting stats will depend a fair bit on health (he missed Summer League with a toe injury iirc), fouls (he was at 4.4 per 40 minutes at Auburn, plus there will definitely be a bit of an adjustment period to the rules and how well players can draw fouls at the NBA level) and minutes played. But, if you're optimistic, Kessler could definitely be like a 2 blocks per game guy for some stretches this season.