There seems to be a lot of confusion as to how frequently each body part can be trained and thats understandable because this is definitely a scenario where one size does not fit all.
There are many contributing factors that can determine whats optimal for your individual needs but generally both training experience and lagging body parts you would like to bring up will be the primary things to consider when choosing how frequently you train each body part. Muscles usually take 48-72 hours to recover so this is good timeline too gauge off when programming your workout.
Now if the event of a lagging body part you would like to bring up I highly recommend prioritising it and training it every third or fourth day. Most common workout splits are generally over a period of four or five days so adding in an additional session for the trouble areas should be no problem at all.
If you happen to have more than one lagging part alternatively you can do both in one session and decrease the workload/volume but increase the intensity to compensate. Am/Pm splits could be another option but not everyone has the luxury of being able to do that so the first option will provide more than sufficient results.
Personally I recommend just choosing one body part to focus on but if you happen to have a rather dominant part, alternatively you could train the dominant part every second split and through in your secondary lagging part in that slot.
If you are just staring out, a classic push/pull/press split with one or two days rest between splits will work wonders in terms of building muscle/hypertrophy. If you are looking to pick up the pace a little more then a chest/tri, back/bi, shoulders/abs, legs routine will be your go to split. For the advanced athlete training everything individually will ensure you are fatiguing the muscles 100%, this will provide a much more intense stimulation and breakdown of muscle fibres which in turn leads to more muscle fibres being built providing your diet can support the stimulus given.