What adapter do I need for a brand new mac book pro to connect to an older mac monitor?

That depends on what type of connector the "older" monitor has. The new Macbook Pro has USB-C / Thunderbolt 3 ports. So look for a Thunderbolt 3 to (old monitor port) adapter.

You may even need to chain 2 adapters depending on age of monitor.

Phil0124 wrote:

You may even need to chain 2 adapters depending on age of monitor.

CAUTION: If you find yourself having to "stack" two adapters to get it to work, PLEASE post back here before you pay for them. "Stacking" adapters is rarely a recipe for success.