As someone with alexithymia, I have found DBT's handouts on "Understanding and Naming Emotions" really helpful in being able to tell what emotion I was having to then validate it or manage it. They are detailed. On each emotion page, Marsha Linehan (long may she live) put things under the following headings, to create a detailed emotion profile:
[Emotion] words - synonyms for and variations of the main emotion e.g. under anger is fury, outrage, resentment, bitterness, annoyance, frustration, hostility, etc
Prompting events for feeling [emotion] - so for anger some prompting events could be "having an important goal blocked," "you or someone you care about being threatened or attacked," etc
Interpretations of events that prompt feelings of [emotion] - similar to above, but it is thought patterns or beliefs that could prompt having a feeling - an example for anger is "ruminating about the situation that caused the anger in the first place"
Biological changes and experiences of [emotion] - so for anger, bodily experiences like fast breathing, a tightness in your chest, tensed muscles, being unable to stop crying - and urges you might get, like wanting to hurt someone
Expressions and actions of [emotion] - just what it sounds like. For anger some examples are: walking heavily, stomping, slamming things; brooding or withdrawing from others; mean expression; physically or verbally attacking someone; crying; grinning
Aftereffects of [emotion] - what happens after the first intense wave of emotion finishes. For anger it includes: narrowing of attention, ruminating about past and imagined future situations that could make you angry, depersonalisation and dissociative experiences
I tend to slowly scan each part of my body for physical sensations, body language, and urges (ie "biological changes and experiences") and then try to match those to an emotion, now that I have those cheat sheets. Getting good at this took a lot of practice and repetition. For me at least, it is a manual skill I have had to build up.
Working backwards to figure out what emotions you might logically have in response to an event and seeing if those match what you are feeling can be really helpful too.
You can find these DBT emotion handouts here (scroll to page 7 for the start of the emotion profiles):
And here is every single DBT handout from the official manual for anyone interested (don't sue me pls):
Also helpful to other people I have talked to is this emotion-sensation wheel by Lindsay Brahman, which some people find easier to follow:
Just don't do a me - I took this too literally at first and thought that only the sensations directly branching off the emotions made up those emotions. In reality there is a lot of mixing and matching, and a lot of stuff not covered on the wheel. It is a rough (but often useful!) guide.
And here is another useful infographic that comes from this article by Greatist, which they adapted from a 2014 study that aimed to map bodily sensations of emotions. Yellow areas are the most activated/tense regions (so they might feel hot, tight, tense, full of energy, warm, maybe sick or fluttery if it is your stomach), and blue areas are the least activated regions (feel heavy, hard to move, maybe weak or cold)
And finally a tip for my neurodivergent friends: when you are scanning your body for emotions, look for signs or causes of overstimulation first, and address that before you try to do any of this - headphones, leaving a space, eating or drinking, turning off lights, weighted blankets, going somewhere cooler or warmer, stimming, whatever you need/can reasonably do. In its early stages overstimulation may feel like an intense emotion, and unfortunately mixing them up can lead to some bad and unproductive times.