It is officially called shrug or person shrugging. Emojipedia, the ultimate reference work in these questions, has this entry:
A person shrugging their shoulders to indicate a lack of knowledge about a particular topic, or a lack of care about the result of a situation.
Displays as raised shoulders, sometimes in conjunction with raised arms and flat hands. The shrug gesture in text (emoticon) form is known as the shruggie and typed as: ¯\_(ツ)_/¯
Person Shrugging was approved as part of Unicode 9.0 in 2016 under the name “Shrug” and added to Emoji 3.0 in 2016.
The Unicode documentation lists it here with the code U+1F937, and in addition to the CLDR Short Name person shrugging, it lists these Other Keywords: doubt | ignorance | indifference | person shrugging | shrug. (CLDR stands for Common Locale Data Repository.)