JSFiddle - React, Tailwind, and code Playground

JavaScript

const emailCount = {
  'vik@g.com': 4,
  'sri@y.com': 9
};

const emailDetails = [{
    'emailId': 'vik@g.com',
    'name': 'Alision',
    'subject': 'hello'
  }, {
    'emailId': 'sri@y.com',
    'name': 'Hanumant',
    'subject': 'ola'
  },
  {
    'emailId': 'ally@o.com',
    'name': 'Brian',
    'subject': 'namaste'
  }, {
    'emailId': 'vik@g.com',
    'name': 'Alision',
    'subject': 'hello'
  }
];

let output = {};
Object.entries(emailCount).forEach(([key, value]) => {
	output[emailDetails.find(item => item.emailId === key).name] = value;
})

console.log(output);