If you want to sort by position 28, this is the way to go :
sort -t \0 -k 1.28 file
id - 884209 , researchers - 1
id - 904091 , researchers - 1
id - 905525 , researchers - 1
id - 916197 , researchers - 1
id - 910480 , researchers - 10
id - 901026 , researchers - 15
id - 896781 , researchers - 4
id - 908660 , researchers - 5
id - 908876 , researchers - 7