During his stay in Berlin in 1764, Boswell lived in the house of Karl David Kircheisen, the president of the Berlin city council.
Gijsbertus Bonnet - Theologian
Gijsbertus BonnetBorn 1723
A pupil of Johannes Horthemels (1698-1776), Bonnet became Professor of Theology (Divinity) at Utrecht. According to sources, he was an outspoken orthodox professor who, among other things, was supervisor of Johannes Clarisse's Doctor of Divinity degree.1
Boswell met him at Heer van Zuylen's on January 30 or February 6, 1764. Boswell "was very much surprised to find him a lively and cheerful man", and ended up borrowing the Professor's copy of Lambert ten Kate's Aenleiding tot de kennisse van het verhevene deel der Nederduitsche sprake - an early philological masterpiece, "in which the connection between the Low Dutch, the Old Saxon, the Icelandic, and the Latin languages is exhibited" (according to Boswell). Boswell went to one of his lectures on May 22.
Note 1: According to Azn, Jasper (2000). The Dominating Theology Within the Nederlandse Hervormde Kerk after 1815 in its Relation to the Secession of 1834.
I don't know of any existing works of Bonnet, but Lambert ten Kate's Aenleiding tot de kennisse... is sometimes available via the AbeBooks.com used books search engine.