I would like to learn how to read medieval Latin manuscripts, but they often use abbreviations/shorthand. What are some books that would help me read these manuscripts?
The UK National Archive runs a two part course which gives immediate feedback and quickly introduces .1. dating of mss .2. different styles of writing (book script, private notes, .3. post classical grammar .4. some abbreviations. You'll whizz through that.
For simply the Abbreviations also known as Sigla
For manuscripts earlier than 850, including a section on Irish Latin, by W M Lindsay posted by InternetArchive
For later Medieval works Kansas University has posted Adriano Capelli (60 page A5) hand book as a pdf
There is one book that you would find more useful than any other, and that is a Latin Bible.
The internet provides access to Manuscripts from the British Library, and the Beinecke (Yale), and the Parker Library (Cambridge) and several others.
So, visit the British library, and tell them you want to read St Cuthbert's copy of St John, Add MS 89000 in half uncials (800) with few abbreviations.
Then move on to the Stavelot Bible (Add MS 28106 1093-1097) The script has developed and there are abbreviations for per- pro- ; -us -um;
And so on through the Centuries. The search engine allows you to chose a date; select Psalms, Gospels, Bible.