There are all manner of ways to measure engine temperatures and not just oil.
You can get an Oil temperature gauge to see what the oil is getting up to. I have done that on race bikes to be safe, until I know that they are OK and then I take it off.
CHT. That's cylinder head temperature and it consists of a dial and a lead with what looks like a washer on the end to measure the temp under the plug. The "washer" creates a current when it's heated. It's a thermocouple. I tend to use them when setting up a rebuilt motor to make sure both sides or all three or four are similar temperatures.
EGT. Another thermocouple but this one is a probe that is inserted into the exhaust pipe to measure exhaust pipe temperatures.
The problem with them all is that on the street there's not much time to be looking at extra gauges and when something goes wrong it tends to happen quite fast.
I find them to be better as diagnostic tools. Last time I had a truck meltdown, there were no signs noises etc . I happened to look down to check my speed and the temperature gauge was off the dial. I was on the highway so there's enough time to glance at the gauges from time to time. On a bike in traffic, not so much.
Back to your question, Daytona used to sell an oil temperature kit consisting of a gauge and a bolt that replaced the drain bolt and had a thermocouple fitted. You can buy sensors and gauges from any auto shop and get an adapter to fit their sensor into your bike. Just google Oil temperature gauge. Here's a few to get you started.
VDO 12v Oil Temp Gauge | CampervanCulture.com
VEI Dual Oil Temperature Gauge - egaugesplus
Oil Temp Gauge | eBay
AAM Competition - Nissan GT-R, 370Z Turbo Performance Specialists
GlowShift | Oil Temp Gauges