On which line it is to be reported is the simple question.  How it should be reported is much more complicated.

There are a good number of questions that need to be asked.

• What kind of pension is that?  There are three kinds of pensions in the Netherlands: AOW (similar to OASDI, which you say it is not), company pension (similar to 401(k)), and individual pension (similar to IRA);
• Is the pension from government service and, if so, is your client a US national/citizen?
• Is the pension distribution made as a lump sum or periodic payments?  If in a lump sum, when did your client terminate residency in the Netherlands?  This will, in turn, affect, how foreign tax credit may be applied; and
• What basis does your client have in the distribution (depending on treaty application and position taken on the prior year returns)?