Assalaamu ‘alaikum,

Does any part of the tongue touch any part of the palate when pronouncing ikhfaa’ (of the noon), or is there no contact at all (free floating tongue, except for the sides maybe that always touch/rest naturally)?   If so, which part(s)? For example when saying: minka, the sides of the tongue seem to make more contact when the tongue is moved towards the makhraj of the kaaf, and without doing that it seems very difficult to produce a ghunnah?

Jazaakumul-laahu khairaa.

Wa alaikum assalaam wa rahmatullahi wa barakaatuh
The mouth gets ready to say the next letter during the ikhfa', and the tongue does not touch the palate nor the sides of the mouth, except in the case of the and , here the tongue does actually touch the articulation point of these two letters during the ikhfa of the noon saakinah before them', but not to the point of closing off the sound of the ghunnah. 

Please see the following previous questions and answers for more details and examples:

Wa iyyaakum