If you want to read a vector in a lua script, use the myVector:at(index) function.
See the https://wiki.realmotion.com/RMWiki/index.php?title=Lua_-_Vector for the vector documentation.
And be aware of: “NOTE: All RM Vectors use 0-based indexing. Lua arrays use 1-base indexing.”
RM Vectors are vectors created to interface with RealMotion. They are non-native to Lua, which starts at 1.
Alternatively, maybe the only thing you need is the box Get Item to retrieve any item of a vector.