These are not working in mail.activity_items template, so i'm trying to pass 'uid' value in mail_activity.js file in this template rendering code. I dont have much points to comment on the answers @Rakesh Vadeghar and @Mitul Shingala. 

Thank you very much  for the support. 

Hello

try with below line

<span t-esc="activity.env.user.id"/>

so your condition is like

<t t-if="activity.create_uid.id == activity.env.user.id">

i hope this will helps you.

To get logged in user id  try this 

<p t-field="o.env.user.id"/>