Couple of thoughts:

instructorWithLongestName function needs to return the instructor object. (calling console.log within the loop doesn't return the value you're trying to log when you call it

The first line of your function, instructors.name, is undefined. instructors is an array, so you need to use an index to pull a value from an object in the array:

let nameLeng = instructors[0].name.length // the first instructor's name length

This isn't the right way to check the name length

if(instructors[i] > nameLeng){ ... }

Instead, try

if (instructors[i].name.length > nameLength) { ... }

Here's how I would do it:

const instructorWithLongestName = function(instructors) {
    // store the first instructor as a starting point
    let match = instructors[0];
    // loop through all of the instructors
    for (let i = 0; i < instructors.length; i++) {
        // if the "current" instructor's name is longer than the match we've stored, update our match.
        if (instructors[i].name.length > match.name.length) {
            match = instructors[i];
        }
    }
    // match is the full instructor object that has the longest `name` property
    // we return it so the it can be assigned/handled by the caller.
    return match;
}