Вы используете hasOwnProperty
неправильно:
function checkObj(obj, checkprob){
if(obj.hasOwnProperty(checkprob)){
return obj[checkprob];
} else{
return "Not Found";
}
}
console.log(checkObj({gift: "pony", pet: "kitten", bed: "sleigh"}, "Amir"));
console.log(checkObj({gift: "pony", pet: "kitten", bed: "sleigh"}, "bed"));