how to access a data array within an associative array in jquery?

Using Object.keys might help you. This is a nested loop.. but works

let data = `{
    "1":[{"project_id":1,"project":"IET1"},{"project_id":2,"project":"IET2"}],
    "2":[{"project_id":3,"project":"IET3"}],
    "3":[{"project_id":4,"project":"IET4"},{"project_id":5,"project":"IET5"}]
}`;

data = JSON.parse(data)
const keys = Object.keys(data);

keys.forEach(key => data[key].forEach(project => console.log(project.project_id + " - " + project.project)));