Hide SharePoint list form fields using jQuery/Javascript

Just add jQuery reference and use below lines

Single line/Multi Line

$("input[title$='Col Name']").closest('tr').hide();

Dropdown

$("select[title$='Col Name']").closest('tr').hide();

to show field use below line

$("select[title$='Col Name']").closest('tr').show();

People Picker or any other field

$("nobr:contains('Col Name')").closest('tr').hide();

Readonly text colum:

$("input[title='Col Name']").attr("readonly",true);