SQL Server - Tempdb data/log file placement Currently we got TEMPDB Data (number of data files:2) and LOG file on same drive.

On monitoring we have found I/O issues on TempDB.

We got an extra drive available - should we move the TempDB Log file to new drive or should we move the second TEMPDb data file on the new drive to help us reduce I/O issue?
If you're already certain you have IO contention, start by understanding which files are the cause.

SELECT
    DB_NAME(fs.database_id) AS [Database Name]
  , mf.physical_name
  , io_stall_read_ms
  , num_of_reads
  , CAST(io_stall_read_ms / (1.0 + num_of_reads) AS NUMERIC(10, 1)) AS [avg_read_stall_ms]
  , io_stall_write_ms
  , num_of_writes
  , CAST(io_stall_write_ms / (1.0 + num_of_writes) AS NUMERIC(10, 1)) AS [avg_write_stall_ms]
  , io_stall_read_ms + io_stall_write_ms AS [io_stalls]
  , num_of_reads + num_of_writes AS [total_io]
  , CAST((io_stall_read_ms + io_stall_write_ms) / (1.0 + num_of_reads
    + num_of_writes) AS NUMERIC(10, 1)) AS [avg_io_stall_ms]
FROM
    sys.dm_io_virtual_file_stats(NULL, NULL) AS fs
INNER JOIN 
    sys.master_files AS mf
ON  fs.database_id = mf.database_id
AND fs.[file_id] = mf.[file_id]
ORDER BY
    avg_io_stall_ms DESC
OPTION
    (RECOMPILE) ;


With the data from that query you can judge whether the log or data files are the point of contention in tempdb. It's probable you'd be better off with both data files on one drive and the log file separate, but you'll never know without the numbers to back the decision.