reading XMP data from stills

I am creating a slideshow from a lot of photographs of local artworks and I want to display the title and artist for each which is currently stored in the XMP metadata of the images.

Is it possible to read this data from the photographs and pass it to Text+ to overlay it on the image?

Not currently.

(I don't know scripting, however.)

Only through scripting. The simplest way to implement this without any use of Resolve API is to write a script that converts the XML metadata of interest to an .SRT subtitle file. This assumes that in your slide show all slides have the same duration.