Hello - my student has a placement outside of our district and his zoned school provides the transportation to the out of district placement. When the zoned school has a snow day but the out of district school does not, whose responsibility is it to provide transportation? Same question when the zoned school has holidays that the placement does not.

Great question!  I haven't come across this issue or researched it, but my thought it that since it is the home district's responsibility to implement the IEP, it would be their responsibility to provide transportation whenever the out of district placement has school and the student is expected to attend.  However, from a practical standpoint, I would give a little grace depending on what the transportation is.  Such as if it's a school bus and under their contracts the drivers don't drive on certain days, etc., or if it's a cab or Uber that can't get there due to snow, etc.

BTDT.  We were told that transportation would only happen on the days the district was in session.  We had to provide transportation on other days.

Rules will vary by state so it's hard to say what applies in your situation.  My state's rules are the district has to transport to charter schools.  Other school situations are on a case-by-case basis.  You can ask for reimbursement for travel expenses when this happens.  This should be in the IEP if the district is reimbursing.