None. (Why do people keep asking this question on AB ?) The difference in Latin is only that temel is 'te' (thee) with '-mel', a suffix ,used mostly in poetry, which refers back to 'te' and makes the meaning 'thyself'. 'Nosce' is 'know' in the form of an edict or command, so 'temel nosce' means 'Know thyself'.
'Nosce te ipsum' means the same but instead of using 'temel' the writer has chosen to use 'te' and 'ipsum', and 'ipsum' in this context, means 'self'' so it's 'Know thyself'