Soul Speed can be obtained inside stronghold chests.

Summary

Soul speed enchanted books can be found in stronghold library room chests. 

Steps to reproduce

1. Use the /locate command to find a stronghold
2. Find a library inside the stronghold
3. Open the chests. 
4. Repeat steps 1-3 in another world for several more times if you can't find a soul speed book (can't provide a consistent seed due to MCPE-72432)
5. The enchanted book will contain the soul speed enchantment.  

Expected Results

Soul speed should not be obtainable through stronghold library chests

Observed Results

Soul speed can obtained through stronghold chests. 

Screenshots/Videos Attached: Yes