How to check when statistics was last executed?

For your edit - You need to enclose table name into single quotes:

EXEC sp_autostats 'tablename'

and for the original question

First - find the statistics you want to check:

Second - see its properties, and there you will see the last updated timestamp:

Or you may want to execute the following query:

SELECT t.name TableName, s.[name] StatName, STATS_DATE(t.object_id,s.[stats_id]) LastUpdated 
FROM sys.[stats] AS s
JOIN sys.[tables] AS t
    ON [s].[object_id] = [t].[object_id]
WHERE t.type = 'u'

The best way to get information about statistics is through the command

DBCC SHOW_STATISTICS (<tablename>,<indexname>)

That will return information not just about when the stats where updated, but their size, density, how selective they are, and the histogram that shows the distribution of data. With all that, you can determine if those stats are up to date and effective.