Can you tell me the composition by percentages of Forney ITEM# 38106?

Lead is shown on the Safety Data Sheet (SDS) as 80 – 100%, Tin is between 1 and 5%, and Metal between 1 and 5%.

You can also see the SDS on the product page here: https://www.forneyind.com/products/solder–general-purpose-repair–solid-core–1-8–16-oz