The IBM Programmer's Toolkit, included in Workset/2, includes a complete on-line syscall reference.
You can FTP the documentation for the 16-bit calls (IBM does not supply them), such as Vio*(), Kbd*(), Mou*(), from cdrom.com as os2/2_x/program/inf16bit.zip.
You can order the seventeen volume IBM OS/2 Technical Library (possibly at a discount, see question 1.2) and/or order various volumes individually.
Most of these volumes are now published by Que books also, and can be found in many bookstores.
All this information is also on the OS/2 Online Library Omnibus Edition:
OS/2 Collection CD-ROM (SK2T-2176), and the Professional Developer's Kit
CD-ROMs have this information as well.
Related Information:
What are good reference books
for programming in OS/2 and PM?