Hi, welcome to Silkysteps
I'm not sure you should be looking for anything particular, the observation itself will involve noting the time of day, place of observation, age of child, possibly gender. Number of adults present - what happens during the lesson - eg: warm up period and rest, instructions given, equipment available, how it is used and interaction between other children / peers in the group - no Child must be identified by name. One example is to record interaction by titling individuals as 'Child A - who will be the Child you are observing and for others - Child B / C / D ..
For your own information & to help keep track of expectations you could note a separate introduction to the observation, if you've maybe had a chat with the teacher beforehand and if they were hoping to introduce any particular 'theme to the lesson or hope to achieve a particular outcome, eg an obstacle course or to learn positioning for a new skill or game.
The importance of observations is to be very objective, only ever state the facts not guess or give reasons why certain things might of happened or word things to intentionally/unintentionally place blame or judgement.
This
narrative observations thread may help
Hth, enjoy the site and your observation
xx