When
BTC Bitcoin pumps in 2020 after halving, what effect will it have alt coins?

I think no need to wait 2020 for bitcoin halving, I still believe bitcoin bullrun coming this ber month for these year... Anyway 2019 is possible to key of the bullrun for the first month of 2020 for bitcoin halving continually and the effect for this in altcoins is possible to bring some altcoin into better place and price position but not all altcoins can give better profits.
after halving one point must be happen on bitcoin is the price of bitcoin are going to the moon and about altcoin maybe their price are going down and try to adjust to the current state of the market and the bitcoin rate
Sorry do not be offend mate, not all altcoins are pump ups, but some of that is have potential to follow into bitcoin if their price are goes into the moon, for sure ethereum is the best coins to hold for loong term.