If the material is large enough, this can be observed using an electron microscope.
[1] Trans-endocytosis from neurons to glia has been observed using time-lapse microscopy.
For example, this process is involved when a part of the protein Notch is cleaved off and undergoes endocytosis into its neighboring cell.
[3][4] Without Notch trans-endocytosis, there would be too many neurons in a developing embryo.
[5] Trans-endocytosis is also involved in cell movement when the protein ephrin is bound by its receptor from a neighboring cell.