I have been divorced for 9 years--- I have 2 children- age 15 and 19, my ex and I share custody- split all expenses- educational, medical, etc. we alternate years that we claim each child as a dependent so for 2016 I will claim my 15 yo son, my ex will cl

What is your tax question? You have not completed your statement nor have you actually asked a tax question.

Yup.  Rest of question didn't get transmitted... so my ex will claim my 19 yo daughter for 2016 so does that mean I can't deduct the college or medical expenses I paid for her ?

Yep ... the college expenses stay with the dependent exemption just like the Child Tax Credit does for the children under the age of 17.  The EX gets to claim all the education expenses ...even what you paid.

Thank you -  very helpful

That is exactly what it means. You can deduct medical expenses and education expenses only for yourself, your spouse, and for your dependents.
You will find the rules for claiming medical expenses in IRS Pub. 502, at this link:
IRS Pub. 502, http://www.irs.gov/pub/irs-pdf/p502.pdf
and you will find the rules for claiming education expenses in Tax Benefits for Education at this link;
http://www.irs.gov/pub/irs-pdf/p970.pdf