Use the .map() array method as follows:

function nicknameMap(p) {
    return p.map(({name,age}) => `${name}-${age}`);
}
//output
//[
//  "ninny-19",
//  "albert-20",
//  "daniel-60",
//  "bob-20",
//  .....
//]

function nicknameMap(p) {
    return p.map(({name,age}) => `${name}-${age}`);
}

const p = [
  { name: 'ninny', age: 19},
  { name: 'albert', age: 20},
  { name: 'daniel', age: 60},
  { name: 'bob', age: 20},
  { name: 'wilfred', age: 40},
  { name: 'rob', age: 22},
  { name: 'gary', age: 9},
  { name: 'robin', age: 19},
  { name: 'carl', age: 43 },
  { name: 'v', age: 82 }
];

const nicknames = nicknameMap(p);
console.log(p);
console.log(nicknames);

function nicknameMap(p) {
  let result = Array();
  p.forEach((n) => {
    result.push(`${n.name}-${n.age}`);
  });
  return result;
}

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push

It's best to learn by yourself, but I'm assuming you've had a crack at it and are asking because you have run out of options.

EDIT: amlxv solution is a more "Javascript" way of doing it, and is technically more correct than mine.

Below is a solution to your problem.

function nicknameMap(p) {
    let arr = [];
    
    for(let i = 0; i<p.length; i++){
      arr.push(p[i].name + "-" + p[i].age);
    }
    
    return arr;
}

const p = [
  { name: 'ninny', age: 19},
  { name: 'albert', age: 20},
  { name: 'daniel', age: 60},
  { name: 'bob', age: 20},
  { name: 'wilfred', age: 40},
  { name: 'rob', age: 22},
  { name: 'gary', age: 9},
  { name: 'robin', age: 19},
  { name: 'carl', age: 43 },
  { name: 'v', age: 82 }
];

const nicknames = nicknameMap(p);
console.log(p);
console.log(nicknames);