The const keyword is only a hint to a C compiler that the function is not modifying the buffer past in in any way. This allows a C compiler to do some optimizations in certain circumstances when calling such a function and when compiling the function any well behaved compiler should complain if you modify this pointer inside the function or pass it to a function which is not itself declared to treat this pointer as const. For LabVIEWs Call Library Node you can fully ignore this keyword.
The void* pointer is a C syntax for a pointer which can potentially point to any datatype. In LabVIEW you will have to find out what the datatype is, this pointer should point at. It could be a byte, short, integer, long, or floating point value or an array of them or maybe also a string and configure the Call Library Node accordingly. LabVIEW is a strict datatype language and does not really allow for ambigues datatypes such as void* do present. This is no problem as the function in question will expect some specific datatype anyhow, possibly depending on a second parameter which defines what datatype the void* parameter should be treated as in this case.
Rolf Kalbermatter
Rolf Kalbermatter
My Blog 
DEMO, Electronic and Mechanical Support department, room 36.LB00.390