One best Selenium Training that I have come across is provided by Edureka.
Do check it out Selenium Certification Training & Course With Project
There are a plethora of training institutes available that offer this course worldwide. I prefer online training to conventional traditional offline training centers.
Edureka's Selenium Certification Training will help you in mastering the various concepts of Selenium from scratch.
This Selenium Training will help you master important concepts such as TestNG, Selenium IDE, Selenium Grid, XPath and Waits, IFrames and Alerts in Selenium WebDriver, POM Frameworks and so on.
This Selenium Certification Training is also a gateway towards your Automation testing career. The course has been curated by industry experts.
Hope this helps!