Get SharePoint fields internal name

Use this powershell command:

$list = (Get-SPWeb "http://portal.contoso.com").Lists["Demo List"]
$list.Fields | ?{$_.title -eq "Title"} | FT Title, InternalName

Example:

PS C:\Users\spt.prod.installer> $list = (Get-SPWeb "http://emflow").Lists["work items"]
PS C:\Users\spt.prod.installer> $list.Fields | ?{$_.title -eq "Title"} | FT Title, InternalName

Title                                   InternalName
-----                                   ------------
Title                                   Title
Title                                   LinkTitleNoMenu
Title                                   LinkTitle
Title                                   LinkTitle2

PS C:\Users\spt.prod.installer> $list.Views | FT viewfields

ViewFields
----------
{Activity_x0020_ID, Status, Entry_x0020_Date, SLA_x0020_Date...}
{Modified, Activity_x0020_ID, Status, Entry_x0020_Date...}
{Modified, Activity_x0020_ID, Assign_x0020_Bucket_x003a_Group_, Entry_x0020_...
{Activity_x0020_ID, Status, Entry_x0020_Date, SLA_x0020_Date...}
{Modified, Activity_x0020_ID, Assign_x0020_Bucket_x003a_Group_, Entry_x0020_...
{Modified, Activity_x0020_ID, Status, Entry_x0020_Date...}
{Activity_x0020_ID, Status, Entry_x0020_Date, SLA_x0020_Date...}
{Activity_x0020_ID, Assign_x0020_Bucket_x003a_Group_, Entry_x0020_Date, SLA_...
{Activity_x0020_ID, Assign_x0020_Bucket_x003a_Group_, Entry_x0020_Date, SLA_...
{Activity_x0020_ID, Status, Entry_x0020_Date, SLA_x0020_Date...}
{Activity_x0020_ID, Status, Entry_x0020_Date, SLA_x0020_Date...}
{Activity_x0020_ID, Status, Entry_x0020_Date, SLA_x0020_Date...}
{Activity_x0020_ID, Status, Entry_x0020_Date, SLA_x0020_Date...}

PS C:\Users\spt.prod.installer>