Want to convert list items into sqlparameter's...

There are a few possible answers to your question. If the list of product IDs are coming from a database, you're best bet is to change your query to either use a JOIN or an EXISTS with a sub-select (using whatever WHERE clause limits the product IDs to the desired ones).

If the list can be long, and is not coming from a database, I would suggest using a stored procedure with a table valued parameter and then pursue the same technique suggested above. For more information on table valued parameters, see:

Use Table-Valued Parameters (Database Engine) | Microsoft Docs[^]

While generally not a good approach, if you know your list will be short and merely want to construct a command with parameters (to avoid SQL injection), something like the following should work:

var builder = new StringBuilder(1024);
int count = list.Count;

builder.Append("SELECT * from Emp where empID in (");
for (int index = 1; index <= count; index++)
{
  if (index > 1)
    builder.Append(',');

  builder.Append($"@p{index}");
}
builder.Append(")");

using (var command = new SqlCommand(builder.ToString(), connection))
{
  SqlParameterCollection parameters = command.Parameters;
  for (int index = 1; index <= count; index++)
    parameters.AddWithValue($"p{index}", list[index]);

  // Do what you want with the command
}